Hillary Clinton encountered rougher seas Sunday night in her latest meeting with her rivals for the Democratic presidential nomination. Both Sen. Bernard Sanders and former Gov. Martin O'Malley questioned her veracity and intensified their criticism of her policy positions and campaign financing.

This was the last time these candidates will debate before the Iowa caucuses on Feb. 1. But the mood of this meeting was more portentous than those of their previous three debates, if only because Iowa no longer looks like an easy win for Clinton. She has seen almost all her polling advantage vanish in that state. She also continues to trail in polls in New Hampshire, which will hold a primary on Feb. 9.

The Sunday night debate was held in Charleston, S.C., which will hold its Democratic primary on Feb. 27. The event was co-sponsored by NBC, YouTube and the Congressional Black Caucus Institute.

O'Malley was included despite his rather humble standing in national polling (an average of roughly 2 percent support among Democrats) because he did reach the 5 percent in Iowa. By the rules for inclusion, that was sufficient.

All three candidates paid tribute to the Martin Luther King Jr. holiday by citing King's influence on their lives. Issues of specific interest to African-Americans surfaced often through the nearly two-hour event.

All three candidates talked of inequities in the criminal justice system affecting black men in particular. Sanders generally agreed on these points and also said any death in police custody should automatically trigger an investigation by the Justice Department. Asked why he was trailing Clinton by more than 2-1 among black Democrats, Sanders replied with a recitation of how well he was doing in other polls and how far he had come.

African-Americans, he said, would come along once they got to know him and his issues. Among those issues was his repeated critique of Wall Street banks and of the campaign finance system, which he said perpetuated income inequality and other distortions of the nation's economic life.

"When the African-American community becomes familiar with my congressional record," said Sanders, "and with our agenda, and with our views on the economy, and criminal justice — just as the general population has become more supportive, so will the African-American community, so will the Latino community."

Clinton, when asked what issue she wanted to talk about but had not been asked about, cited the lead poisoning crisis in Flint, Mich., an older industrial city with a largely African-American population. A recent decision to use river water there has led to widespread lead poisoning, including nearly all the city's younger children.

Sanders began the debate on the defensive regarding his past stands on gun rights and immunity for gun makers.

"He voted for immunity from gun makers and sellers which the NRA said was the most important piece of gun legislation in 20 years," said Clinton. "He voted to let guns go onto Amtrak, guns go into national parks. He voted against doing research to figure out how we can save lives."

Said Sanders in reply, "I think Secretary Clinton knows that what she says is very disingenuous," adding that he only had "a D-minus rating from the NRA" so he couldn't be that good a friend.

Sanders then took the fight to Clinton on a number of other issues — especially the regulation of Wall Street, her ties to Wall Street banks, including $600,000 in speaking fees from Goldman Sachs.

Clinton at several points defended her stands by linking them to President Obama's — an ironic tactic given her bitter fight with him over the 2008 nomination.

"The comments that Sen. Sanders has made," said Clinton, "[they] don't just affect me, I can take that, but he's criticized President Obama for taking donations from Wall Street, and President Obama has led our country out of the Great Recession."

And she did not leave it there.

"Sen. Sanders called [Obama] weak, disappointing," Clinton said. "He even, in 2011, publicly sought someone to run in a primary against President Obama."

She highlighted her work with Obama on foreign policy as his secretary of state (2009-2013) and argued for maintaining and defending Obamacare rather than reaching for a Sanders-style revision of the system that she said would "force the country back into another contentious debate."

Sanders said he would be replacing existing government programs and private insurance with what Franklin D. Roosevelt had wanted: "health care for every man, woman and child as a right."

To finance the government as the new "single payer" for health care, Sanders would raise taxes substantially on higher incomes in the U.S., imposing rates of over 50 percent on the incomes of the wealthiest. Capital gains would also be taxed at the same rate as wages and other forms of income. The payroll tax that now covers Social Security and Medicare would also be enlarged and extended to more income that is currently exempt, were Sanders to prevail.

"It's one thing to say I'm raising taxes," said Sanders. "It's another thing to say that we are doing away with private health insurance premiums. So if I save you $10,000 in private health insurance and you pay a little bit more in taxes in total, there are huge savings in what your family is spending."

Foreign affairs came up at several points but did not dominate the evening as in some of the Republican debates. The candidates noted that several individuals with dual American-Iranian citizenship who faced prison terms in Iran had been released over the weekend after 14 months of negotiations between the two countries.

The U.S. has also just lifted sanctions on that country pursuant to the larger agreement negotiated and completed in 2015. Those arrangements, and the easing of legal cases brought by the Justice Department against several Iranians, had been roundly criticized by several Republican candidates for president on Sunday.

Clinton in particular praised her successor, Secretary of State John Kerry, for his efforts to free WashingtonPost reporter Jason Rezaian and the other detainees and for negotiating the recent nuclear agreement with Tehran.

Much of the social media attention paid to the debate focused on the more aggressive tone and approach taken by all three contestants. Sanders had been urged to drive home his contrasts with Clinton to close the sale in Iowa and New Hampshire. He was expected to do that in part because the Clinton campaign had sharpened its own attacks on him in recent days.

Chelsea Clinton had accused him of trying to "dismantle" the existing health care system, and a superPAC run by a Clinton ally had run an ad asking whether Sanders, now 74, is healthy and vigorous enough to serve four or eight years in the Oval Office.

The heightened tension also reflected the relatively unsettled state of the race. After months of seeming the clear favorite and likely nominee, Clinton has seen her national approval ratings fall in the past month. And while Sanders has not risen to a corresponding degree in national polls, he has improved his standing in both Iowa and New Hampshire.

A resident of Vermont for nearly half a century, Sanders has always had a certain appeal to Democrats, especially the more liberal ones, in neighboring New Hampshire. But his ascent in Iowa, where he began with far less name recognition, has raised eyebrows throughout the political world. It was in Iowa that Barack Obama began his string of upset victories over Clinton in 2008, when she had once been thought nearly as inevitable as she seemed last fall.

Hillary Clinton maintains leads in some national polls of Democrats and those who lean toward the Democrats. The latest reading by the respected tandem of NBC and The Wall Street Journal most recently found her ahead of Sanders by 25 points countrywide. But last week a CBS News/New York Times poll had her national edge at just 7 points.

All agree that in Iowa and New Hampshire the race is too close to call. Clinton has a lead of four points when all Iowa polls are averaged, while Sanders has a six-point advantage by the same measure in New Hampshire. Sanders found a moment to crow about this:

"As Secretary Clinton well knows, when this campaign began she was 50 points ahead of me. We were all of three percentage points. Guess what? In Iowa, New Hampshire, the race is very, very close. Maybe we're ahead [in] New Hampshire."

Clinton seems comfortably ahead in the next two states that also test party sentiment in February — Nevada and South Carolina. But such leads have melted away in the past when a frontrunner has failed to win in Iowa or New Hampshire.

In 2008, the last time the Democrats had a contested nomination, Clinton saw her early polling dominance challenged when Obama, then a senator from Illinois, gained a solid win in Iowa. Even though Clinton recovered to win in New Hampshire the following week, her support declined in South Carolina and Nevada. This enabled Obama to gain the upper hand, fight her to a draw on the big primary day (Super Tuesday) and then outlast her through the spring.

Could that happen to Clinton again this year? It seems less likely, as Sanders lacks Obama's natural advantage among African-Americans and other minority voters in South Carolina and elsewhere. So even if he wins both Iowa and New Hampshire, he might still struggle in the later February states. Thereafter, as the contest move to other Southern states on March 1, black voters will continue to represent a larger portion of the Democratic turnout.

O'Malley could also be a factor in the Iowa contest, which is conducted as an open caucus at the precinct level. At these events, caucus participants hold a preliminary vote, and candidates whose support falls short of a viability threshold are dropped. Their supporters are then free to support others in the final vote. So in those precincts where O'Malley has backers, but not enough to qualify for the final vote, the second-choice preference of those backers could prove critically important. A similar dynamic has made a difference to the outcome in the Iowa caucuses in some recent cycles — notably 1984, 1988, 2000, 2004 and 2008.

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