Biden's string of primary victories over Sen. Bernie Sanders, I-Vt., has improved the outlook of many Democratic strategists, who had feared that a Sanders nomination, which looked increasingly possible, would make winning the general election more difficult and could threaten down-ballot candidates, as well.
Biden's campaign has begun to shift its focus to the general election even as the nomination contest with Sanders continues. The two Democrats will debate Sunday night on CNN and face another round of primaries on Tuesday. In those four contests - Arizona, Florida, Illinois and Ohio - Biden is heavily favored and likely to add to his growing lead in delegates.
Both the Trump campaign and Democratic strategists have been focused first on the four key states that made Trump president in 2016: Michigan, Pennsylvania, Wisconsin and Florida. The campaigns also expect to compete in North Carolina, Arizona, Minnesota and possibly one or two other states in an effort to expand their paths to an electoral majority.
Biden's sizable victory in Michigan on Tuesday, powered by a sharp rise in suburban turnout and strength across the state, has generated a surge of optimism and some cautionary warnings among Democrats about their prospects of winning that crucial state and others that will decide the outcome in November if the former vice president is at the top of the ticket. The turnout gave them hope that the energy behind the Democrats' decisive victories during the last midterms could spell trouble this year for Trump.
"The dynamics in Michigan have not shifted from 2018 and that is bad news for the Republicans," said Richard Czuba, an independent Michigan pollster.
The bigger unknown is what political impact the spreading coronavirus could have in November. The massive disruption to daily lives and the meltdown in financial markets are likely to affect voters' views of their own futures and potentially the two candidates as well, but in what ways no one can say.
Judgments on the government's response to the crisis, pro or con, could affect swing voters as they make decisions in the fall, while shocks to the economy and the possibility of a recession could rob the president of the single strongest issue he has had in his bid for a second term.
"Historically there are periods in presidential history where people just want calmness after a storm, said Susan MacManus, emeriti professor of political science at the University of South Florida. "That would be one of the key things is to see, whether Biden can project calmness and competence after the tumultuous period we've been in.
If anything the uncertainty surrounding the coronavirus makes planning for the general election more difficult, but also might open the possibility of other states coming into play by later in the year. Campaigns are only now beginning to assess but lack trustworthy data in the middle of the pandemic to be able to make decisions with confidence.
Tim Murtaugh, the Trump campaign's communications director, expressed confidence about the president's prospects for winning a second term, asserting that the electoral map looks favorable whether the challenger is Biden or Sanders.
"Joe Biden will have a problem with union workers all across the upper Midwest because of his support for the job-killing NAFTA and TPP [Trans Pacific Partnership] deals, so this myth of Biden as some kind of blue-collar hero will be destroyed," he said in an email message. "Biden's support for the public option in health care is just another way of crowding our employer-provided health insurance that people know and value."
Biden's team is operating on painful lessons Democrats learned from 2016 as well as on what could be the new realities of campaigning in a time of a pandemic. "It's incredibly important that we start from a standpoint of how wide the landscape could be," a senior Biden campaign official, who spoke on the condition of anonymity to offer a candid assessment of the race. "It is a detailed belief that I have that you can't take anything for granted . . .. I'm not willing to sit here and say we don't need Florida and Ohio is dead."
Democrats hope for a continuation of the increase in turnout, particularly among suburban women, that helped them win the House in 2018.
Meanwhile, the Trump campaign is counting on increased turnout among voters in areas exurban and rural areas who sat out 2016 but could make the difference in November and also are making appeals to Latinos and African-Americans.
One Biden campaign official said that, because of what the Trump campaign is doing to communicate to voters of color and what likely will be new rules of the road for voter contact and mobilization, the campaign will have to put even greater emphasis than ever in assuring that the party's core voters turn out in November.
That means greater breadth and depth in trying to reach all potential supporters. "We're going to have to do the work of persuasion and get out there and make sure people turnout" the official said.'
Florida appears to be a must-win state for the president and if he successfully replicates his narrow victory of 2016, the three northern states, or equivalent substitutes, become crucial for the Democrats. Of those three, Wisconsin is considered the most difficult.
Democratic strategists see Biden as better positioned than Sanders to reach an Electoral college majority, in large part because the Vermont senator's past and current statements about Cuba and his Democratic socialist agenda would cost him significantly among Hispanic voters in Florida. That doesn't mean Sanders would have no path to 270 electoral votes, only that his margin for error would be smaller than for Biden.
These same strategists say Biden appears able to put together a coalition of African-Americans, suburban women and enough working-class white voters to improve on Hillary Clinton's performance in Pennsylvania, Michigan and Wisconsin, which she lost by a combined 77,000 votes.
But some Democrats are more cautious in their assessments of Biden's prospects. They worry that Trump is working to persuade voters of color either to defect or stay on the sidelines and see a need for the Democratic nominee to engage with those communities as much as they appear to be looking to attract white working-class voters.
The Trump strategy "is to amp up their base with messages that stoke fear across the electorate and draw defection from the Democratic electorate," said Patrick Schuh, Michigan state director for America Votes, a progressive organization. "Democrats and the progressive coalition are energized right now but is running against Donald Trump enough to keep that coalition energized? We have to appeal to both white working-class voters and voters of color."
Florida's primary on Tuesday could offer some clues about the fall campaign, but Clinton routed Sanders there in the 2016 primary and still lost the state to Trump in November. Biden is seen as a stronger candidate in that state than Sanders.
Trump won Florida by just over a percentage point and won each of the three northern states by less than a percentage point and a combined total of just 77,000 votes. He rates as a very slight favorite to win Florida again.
Steve Schale, a Florida-based Democratic strategist who is part of the group that formed Unite America, the super PAC helping Biden, said his state has been through so many close elections at the national and state level that one should expect another in November.
Florida's voting patterns are shifting, but he said the changes have not altered the overall partisan split in the state. "Democrats are doing wildly better in south Florida than before, and Republicans are seeing huge growth in places like Naples and Fort Myers. They keep balancing each other out." He predicted that two media markets in the central part of the state - Orlando and Tampa - will determine the outcome.
Some Democrats worry that Trump has been effective in registering voters who would be partial to the president but did not turn out in 2016. Many of these voters live outside of major population centers. "They have done a good job registered downscale, white voters," said Jim Messina, Obama's 2012 campaign manager. Florida is one and Pennsylvania is another, he said.
Another issue that concerns some Democrats is the potential resistance among some Hispanic voters - Cuban Americans and Venezuelan immigrants - to a Democratic nominee. "It is extremely sensitive territory for members of that community to know that U.S. leaders, especially the president of the United States will stand with them," said one Florida Democratic politician speaking privately. "Biden will have to deal with that directly."
MacManus identified another potential weakness for Biden in Florida. "Over a third of our voters are the two youngest generations," she said. "If they can't be encouraged to turn out and vote for Biden that's a really big problem."
Of the three crucial northern states, Democrats feel best now about Michigan followed by Pennsylvania and then Wisconsin, which is seen as the tipping-point state for November, meaning the state that could give one candidate or the other the 270th electoral vote.
Trump campaign officials have made clear they will compete hard in Minnesota, which Clinton carried narrowly in 2016. Democrats agree that it is a state they must watch carefully because of its demographics. The Republicans will target other states as well but are not likely to carry them unless the president is winning by bigger margins than in 2016.
Democrats long have seen Arizona and North Carolina as targets and believe with Biden as the nominee both are even more attractive because of his potential ability to build a broad coalition.
Former president Barack Obama won North Carolina in 2008 and then lost in 2012 and Trump carried it in 2016. Arizona's changing demographics and a costly and competitive Senate race that Democrats are eyeing make it attractive. If Wisconsin proves too difficult for Democrats, Arizona's electoral votes could compensate.
"Democrats are going to wage holy war to put Arizona and North Carolina into play and recent events have made that more doable," Messina said.
Countering that, Trump's team came close enough in Minnesota in 2016 to warrant a serious investment there. New Hampshire too was quite close in 2016 and given the Trump campaign's vast resources, worth going for. Both sides will treat it as a legitimate battleground, despite its small size.
Republicans also have talked about New Mexico as a state Trump could win but Democrats are skeptical that he can turn the state red. Meanwhile, Biden's team will look seriously at competing in Ohio and even possibly Iowa, even though Trump won both handily four years ago.