The coronavirus pandemic and related economic tailspin is expected to be the top issue that will determine how Americans vote this November, according to top party strategists working on 2020 races.

"We all know that both the health crisis of coronavirus and the economic impact that's followed will likely be the most dominant issue, perhaps the only issue, that voters will be thinking about when deciding who to support in the fall elections," Steven Law told NPR. Law runs the Senate Leadership Fund, the top Republican super PAC aligned with Majority Leader Mitch McConnell.

Republicans currently hold the Senate 53-47, but control of the chamber is in play this November. Law says moments of national crisis can favor incumbents, which could benefit Senate GOP candidates in competitive races in Colorado, Maine and Arizona, among others.

"As we saw after [the terrorist attacks of Sept. 11, 2001], crises tend to advantage the incumbents if they rise to the occasion and do the jobs well," he said. "You've got responsibilities, voters expect you to perform them, and most importantly in a crisis they pay attention to what you're doing." Law said it's much harder for non-incumbents' message to break through to voters, and incumbents can benefit from more media coverage on their response to the crisis.

Something that could also benefit incumbents: There is some indication that a growing number of people think Congress is doing a good job. A Gallup survey last week showed Congress's still-low approval ratings jump by a net gain of 16 percentage points in the past month — its highest point since 2009 — after Congress approved a $2 trillion-plus aid package to address the pandemic.

If the political moment favors incumbents, that is also good news for House Democrats, who are currently favored to hold their majority.

"This is a moment in history and how we as the majority in Congress, how we behave, how we campaign, how we treat people, how we fight for people, all of that will matter come November 2020," said Rep. Cheri Bustos, D-Ill., who is running the Democrats' 2020 campaign operation.

Charlie Cook, a nonpartisan election analyst, said the pandemic puts the impeachment of President Trump further out of voters' minds, which benefits the House Democrats running in Trump-won districts who voted for it. "The more impeachment is in the rear view mirror, the better off they are," he said.

Democrats had already planned to make health care a central focus of all of their campaigns this fall. J.B. Poersch runs Senate Majority PAC, a top Democratic Senate super PAC working to flip the Senate. He said the pandemic has heightened the issue in voters' minds and that will benefit Democratic candidates. "Coronavirus is showing the urgency of the health care debate in real time."

While Democrats have long believed they have the upper hand in elections if health care is a deciding issue, GOP strategist Dan Conston says his party will benefit if voters are focused on the economic turnaround come November.

"A conversation about dollars and cents and economic growth is fundamentally a very good argument for Republicans to be running on this fall," said Conston, who runs the Congressional Leadership Fund, the top super PAC for House Republicans.

He noted the public's views on Trump continue to track largely along familiar partisan lines, and while the president's approval rating will surely be a factor in November, the calculations around it haven't shifted dramatically yet. "It's remarkable just how consistent the political environment has stayed up 'til now," he said.

Tim Phillips, president of the the right-leaning advocacy group Americans for Prosperity, cautions that no one should rely on the usual election year metrics in this moment. "The old measurements: job approval, favorability ratings, the ballot question, people's view on the economy: 'Is it good or bad right now?' I don't think they're going to hold water the way they used to," he said.

Phillips said moments of crisis can depolarize more voters. He thinks the major impact for 2020 will be a much bigger pool of swing voters than strategists were betting on just weeks ago. "Just the sheer scope of what they're experience and the personal manner in which they are experiencing it has made more Americans consider the parties, the candidates and also the issue approaches as well."

The result? "This crisis will make this election cycle the most unpredictable election cycle in modern American history," Phillips said.

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