Updated March 6, 2024 at 12:28 PM ET

There had been a crowded field of Republican choices to challenge President Biden. One by one throughout primary season the GOP candidates dropped out, and with former U.N. Ambassador Nikki Haley's announcement March 6 that she was ending her campaign, only former President Donald Trump remains.

Biden is vulnerable because of questions about the economy and a lack of intensity with the Democratic base. Trump's own vulnerabilities are glaring, but so far he has dominated in primary elections and seems like the inevitable nominee.

Here's a look at the once-deep GOP primary field:

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Running

Donald Trump

Announced: Nov. 15, 2022

Strengths: Former President Donald Trump has a stronghold with a significant portion of the GOP base. He has reshaped the Republican Party in his image, has shown he can raise money and has already won the presidency once.

Weaknesses: Chaos and controversy seem to surround him. Trump was impeached twice and is under investigation in multiple states due to his role in inspiring the Jan. 6, 2021, riot at the U.S. Capitol and for his continued lies about the 2020 presidential election. Majorities have consistently disapproved of the job he did as president and continue to have a negative view of Trump personally.

Dropped Out

Nikki Haley

Suspended her campaign: March 6, 2024

Announced: Feb. 14, 2023

Strengths: Nikki Haley, the former Trump administration ambassador to the U.N. and former governor of South Carolina, was the first candidate to challenge Trump. She's a fresh — and diverse — face on the national scene and will very likely be the only woman in the Republican 2024 presidential field. Haley served in the Trump administration, so she can tout that with the MAGA base, and she is a less abrasive conservative than Trump or Florida Gov. Ron DeSantis. Haley has a record as a governor (from a key early-primary state), articulates the case for Republican leadership well, is the daughter of Indian immigrants and is a couple of generations younger than Trump and Biden.

Weaknesses: Haley is not very well known nationally, and one of her first policy moves soon after announcing her bid was to say Social Security, Medicaid and Medicare should be on the chopping block.

There will also be parts of her record that conservatives will go after, like past, more inclusive statements on immigration and immigrants — despite some harder-line policies she signed on to as governor — in a party that has moved hard to the right on the issue. Then there's Haley's taking down of the Confederate flag at the South Carolina State House grounds after the killing of nine Black parishioners at a church in Charleston, South Carolina. How that will cut is unclear in a GOP primary, as the party has moved to the right culturally.

Ron DeSantis

Suspended his campaign: Jan. 21, 2024

Announced: May 24, 2023

Strengths: Florida Gov. Ron DeSantis is the name on the tips of Republicans' tongues. He has been described as "Trump without the baggage" or "Trump with a brain." (He went to Yale University and Harvard Law School.) At only 44 years old, he's more than a generation younger than the former president. He has been governor of a big state — Florida — and gained prominence for his defiance on COVID-19 regulations, immigration and education. Several state and national polls over the past several months have shown him leading Trump, and while he has not declared his candidacy yet, people in his inner circle may believe now is the time.

Weaknesses: He may be more disciplined than Trump, but he lacks a certain charm. Some have cast doubt on his retail-politicking ability. While his conservative record may play well with many on the right, it's the very thing that may be his biggest weakness in a general election. As a U.S. House member, he was part of the ultra-right-wing House Freedom Caucus and was critical of then-House Speaker Paul Ryan's budget as not making enough cuts. Part of what he supported was a budget that slashed benefits to Social Security and Medicare. But he will also have to contend with anti-abortion-rights activists who believe Florida's 15-week abortion ban didn't go far enough. Generally, he's also untested as a national candidate. To this point, he has made Biden his foe, but how he'll handle the incoming from Republican rivals isn't clear at this point.

Asa Hutchinson

Suspended his campaign: Jan. 16, 2024

Announced: April 2, 2023

Strengths: Asa Hutchinson is Arkansas' former governor, and that executive experience is usually a good launching point for president. He's trying to carve out a position that appeals to Republican-leaning independents, as he's standing against the "chaos" of Trump and has criticized the former president because of his role in the Jan. 6 insurrection. He has a conservative record on taxes and abortion rights, which, on paper, could be attractive to the GOP base.

Weaknesses: Hutchinson's opposition to Trump will make it difficult to win over a significant portion of Trump's base. He also has a fairly dry personality and is on the older side for a presidential candidate, especially for one not already well known nationally.

Vivek Ramaswamy

Suspended his campaign: Jan. 15, 2024

Announced: Feb. 21, 2023 (Here's Ramaswamy's May 2023 interview NPR Politics Podcast)

Strengths: Former tech and finance executive Vivek Ramaswamy is a fresh, young diverse face for most Americans, has a sterling educational background and comes from the business world, which is traditionally valued in the GOP primary. He has been a prominent voice in conservative circles, arguing against the environmental, social and governance (ESG) movement and against "woke"-ism. That could help him with white-collar Republicans, who want an alternative to Trump.

Weaknesses: He's not well known, is very young for a presidential candidate, doesn't start with a solid base of support and will likely have trouble breaking through as a serious major candidate.

Chris Christie

Suspended his campaign: Jan. 10, 2024

Announced: June 6, 2023 (Here's Christie's September 2023 interview with NPR's Politics Podcast)

Strengths: He's a sharp and direct talker, who was once a star with the GOP base. The former federal prosecutor is a good debater who has shown a willingness to take on all comers, including former President Trump. If Florida Gov. Ron DeSantis' star continues to fade, there will be an opening in the other-than-Trump lane.

Weaknesses: His willingness to take Trump on is also his biggest problem. There isn't much room for anyone in the GOP who offends the Trump base, as it is still a significant majority of rank-and-file Republican voters. Christie has also shown a willingness to work with Democrats. He angered conservatives with his embrace of President Obama during Superstorm Sandy, and he has a tendency to make enemies with his sometimes-gruff personality.

Doug Burgum

Suspended his campaign: Dec. 4, 2023

Announced: June 7, 2023 (Here's Burgum's September 2023 interview with NPR's Politics Podcast)

Strengths: He's a fresh face with little baggage nationally. As governor of North Dakota he's cut taxes, rolled back transgender rights and is expected to emphasize his small-town roots. Oh, and he's a billionaire, so money likely won't be an issue.

Weaknesses: Who? Seriously. Burgum has zero national profile and is from a small state. In an already-crowded field, standing out will be tough, especially with other huge personalities blotting out the sun.

Tim Scott

Suspended his campaign: Nov. 12, 2023

Launched a presidential exploratory committee: April 12, 2023

Filed FEC paperwork to run for president: May 19, 2023

Announced: May 22, 2023

Strengths: Tim Scott is Black and from a key early GOP primary state — South Carolina. While he's conservative, his diverse background and upbringing bring a different perspective to the white-dominated Republican Party. The only Black Republican senator can have a commanding presence and has a more optimistic outlook than Trump or DeSantis. He has also hoarded millions of dollars and started to reach out to a national donor base.

Weaknesses: His national profile is lacking, and that will take time and money to build. He also has to contend with the problem that Haley presents, running from the same state with a similar donor set and geographic strength. They could split the vote in the South Carolina primary, opening a path for another candidate. Scott is also untested when it comes to how he will attack another opponent. He's largely seen as a nice-guy candidate. Some of his views are also ultra-conservative and could hurt him in a general election.

Mike Pence

Ended his campaign: Oct. 28. 2023

Pence plans to announce his campaign for president on June 7 at an event in Des Moines, according to a source familiar with the campaign.

Filed FEC paperwork to run for president: June 5, 2023

Announced: June 7, 2023

Strengths: Mike Pence's biggest strength — as well as a big reason he was Trump's vice president in the first place — is his appeal with white Christian evangelicals. They are a sizable portion of the Republican base, especially in Iowa, a critical early-nominating state. He has a national profile and has been involved in a presidential campaign once already.

Weaknesses: Pence's weaknesses are glaring. His break with Trump has made him a bit of a pariah for the MAGA base, and he doesn't have much of a base of his own beyond a segment of white evangelicals. Despite his national profile, he lags well behind the rest of the field in hypothetical matchups.

Will Hurd

Suspended his campaign: Oct. 9, 2023

Announced: June 22, 2023 (Here's Hurd's July 2023 interview with NPR's Politics Podcast)

Strengths: He's smart and young, and wants to talk about the future of the party and the country. He also brings diversity as one of two Black men running for the GOP nomination.

Weaknesses: He's largely out of step with where the heart of the Trump-loving GOP is. He called Trump "lawless" in his announcement video, said he should have dropped out after the Access Hollywood tape was made public in 2016 and he criticized the former president after the white supremacist rally in Charlottesville, Va., and over his administration's family separation immigration policies. Though Hurd voted for a ban on abortions after 20 weeks, he has also looked for bipartisanship on issues from immigration to LGBTQ rights.

Francis Suarez

Suspended his campaign: Aug. 29, 2023

Filed FEC paperwork to run for president: June 14, 2023

Announcement: June 15, 2023

Strengths: Miami Mayor Francis Suarez, who speaks Spanish, brings an added layer of diversity to the Republican presidential field. And Republicans have struggled with Latinos in a demographically changing America. He is young and charismatic, and brings an "aspirational" message, as he calls it.

Weaknesses: Latinos are not a monolith. Suarez is Cuban-American, which could help in a state like Florida, but may have limited appeal in the southwest and other key swing states, where Americans of Mexican descent are crucial. Suarez is also not a household name, and without that name recognition, it is going to be difficult to mount a strong bid for the nomination, especially with Trump blotting out the GOP sun. Being a mayor is also a difficult place to launch a presidential campaign from and he may struggle to raise the necessary money to launch what will be a very expensive effort against well-heeled opponents.

Not Running

Mike Pompeo

Announced he would not run: April 14, 2023

Strengths: Mike Pompeo served as secretary of state and CIA director under Trump — high-profile jobs that upped not only his national but his international bona fides. This gives him a much firmer platform to start from for a presidential campaign than simply being a congressman from Kansas. He's serious and conservative, and his jobs under Trump give him some ability to criticize both Trump and Biden on foreign affairs. He's also close to billionaire conservative donor Charles Koch.

Weaknesses: It's hard to see how Pompeo emerges from the GOP sun-blocker that is Trump. When asked if he'd support Trump in 2024, Pompeo said, "Oh goodness, no," leaving open the possibility of his own run or supporting another candidate. "I'm very hopeful that people won't choose tweets and celebrity, but rationality and arguments. That we'll have a real conversation within our party." Though he had high-profile jobs under Trump, he doesn't have a natural base with any particular segment of the Republican Party, isn't well known nationally and doesn't have a very dynamic personality.

Chris Sununu

Announced in a June 5, 2023 Washington Post op-ed he would not run

Strengths: New Hampshire Gov. Chris Sununu will try to carve out a moderate, anti-Trump lane. He has tried to say that his party needs to move on from Trump and that DeSantis' style of governance is too authoritarian. He's popular in his home state, and his home state just so happens to be a key early-primary state.

Weaknesses: He's not very well known nationally, and he is out of step with a large portion of the GOP base with his socially moderate views. Sununu is largely in favor of abortion rights but supports restrictions later in pregnancies. Yet he has said: "I've done more on the pro-life issue, if you will, than [any other New Hampshire governor]," touting New Hampshire's 24-week ban. Sununu has tried to walk a line on immigration, saying that this is a "country of immigrants," but he has also endorsed DeSantis' migrant flights: "Anything we can do to bring national awareness to it has to be done," he said, noting that he didn't want the migrants sent to New Hampshire, though.

Glenn Youngkin

Strengths: Glenn Youngkin won election as governor in a Democratic-leaning state — Virginia. During his campaign, he was able to strike a balance with Trump. He did not speak out against Trump and he accepted Trump's endorsement, but he did not campaign with him, as he tried to balance winning over Trump voters and swing voters. Many candidates have since been advised to use the Youngkin model. He focused on education and how racism and gender are taught in schools, which has been a cultural touchstone with the base. He's very wealthy — worth almost half a billion dollars thanks to a career in private equity — and has shown he's willing to spend on a campaign.

Weaknesses: It's not clear the model he won on can be replicated nationally and in a presidential-election year. He was able to do what he did in Biden's first year as president, and traditionally, the candidate of the opposite party as the president has an advantage in Virginia gubernatorial races. He's also not well known nationally, and the scrutiny of his business and financial dealings would be intense.

Kristi Noem

Strengths: A feisty favorite of many conservatives, South Dakota Gov. Kristi Noem gained prominence with her administration's opposition to restrictive COVID-19 policies. Her state's largest city, Sioux Falls, has seen strong growth over the last few years, and Noem has gotten a good deal of attention, particularly for a governor from a small state.

Weaknesses: Coming from such a small state is a difficult jumping-off point for a presidential candidate. Fewer than a million people live in South Dakota. Looked at another way, it wouldn't even be in the country's top 40 counties. Noem is untested on a national stage, and with a potentially crowded field of people with higher profiles from larger states, Noem's likeliest shot at the national ticket is making the shortlist for vice president.

Liz Cheney

Strengths: Liz Cheney, Wyoming's former congresswoman and the daughter of a former vice president, is well known and prosecutes the case against Trump well, making her potentially formidable on a debate stage.

Weaknesses: Her intense opposition to Trump, despite her conservative policy bona fides, makes it difficult to see how she could gain enough support to win the GOP nomination. And with the Republican National Committee mandating that candidates pledge to back whoever wins the nomination, in order to participate in its debates, she may never be seen in one.

John Bolton

Strengths: The hawkish former national security adviser under Trump, John Bolton has had a prominent career, serving the last four Republican presidents. He's also likely fairly well known to Fox News viewers, as he regularly appeared on the network. Foreign policy is his area of expertise, and he's likely eager to take on Trump on the subject, given Bolton's sharp criticisms of the former president after he left Trump's administration.

Weaknesses: He has made enemies in both parties and both wings of the Republican Party, including with Trump. That narrows the potential GOP voters open to him. Republicans are also simply not animated right now by an interventionist foreign policy. His age will be a factor as well.

Alyson Hurt and Ashley Ahn contributed to the design and development of this story. It was edited by Megan Pratz and Heidi Glenn, photo edited by Catie Dull and copy edited by Preeti Aroon. contributed to this story

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