The so-called blue wall states — Michigan, Wisconsin and Pennsylvania — had gone to the Democrats in every presidential election since the 1990s until President Trump carried them all in 2016. The three states could again prove decisive as Mr. Trump tries to hold on to the White House.
Early vote totals in Michigan and Pennsylvania show the president ahead, while Joseph R. Biden Jr. edged into a narrow lead in Wisconsin on Wednesday morning. But the numbers were incomplete and did not include some of the largest and most heavily Democratic areas in the states.
Here is a look at where things stand as the counting continues and each state remains too close to call.
Perhaps no state is staring down a longer counting period than Pennsylvania. As of early Wednesday morning, 5.3 million votes had been counted in Pennsylvania, which represented roughly 65 percent of the estimated vote total in the state.
The state legislature refused to allow election officials to begin processing absentee ballots until 7 a.m. on Election Day, and officials across the state were laboring through the tedious process of counting ballots.
In Philadelphia, only 76,000 absentee ballots out of more than 350,000 were processed in the first 14 hours that officials were allowed to count ballots. Though Philadelphia election officials were working around the clock on the absentee ballots, the pace indicated that the count could last into Thursday.
Other major counties, like Chester, Montgomery and Delaware, suburban counties outside of Philadelphia and a growing source of strength for Democrats, also had not reported the majority of their mail-in ballots. Allegheny County, home to Pittsburgh and another Democratic base of support, still had a large share of ballots to count.
Senator Bob Casey, Jr., a Democrat, said, “I’m confident Joe Biden will carry the state because of the margins we’ll get in those counties.”
Though President Trump had a roughly 670,000-vote advantage in Pennsylvania, Democrats in the state were confident that they could make up the margins with turnout from Philadelphia and the “collar counties” surrounding it still outstanding.
They also were buoyed by winning back Erie County in the northwest corner of the state. Democrats had requested more than 1.1 million more absentee ballots than Republicans in the state, according to data from the secretary of state’s office.
The delays in results in Pennsylvania, however, might extend beyond the simple challenge of counting the outstanding ballots. Republicans filed multiple lawsuits in the state on Tuesday, including one regarding provisional ballots for voters who had their absentee ballots rejected.
Early on Wednesday morning, national Democrats filed a motion intervening in Montgomery County. Hearings were scheduled in both state and federal court on Republican lawsuits, and lawyers on both sides were anticipating further litigation in Pennsylvania.
Early returns were inconclusive Tuesday evening, with the key population center of Milwaukee yet to report vote tallies. But early Wednesday, a large vote count from that city was announced, and Mr. Biden edged ahead of Mr. Trump based on roughly 90 percent of estimated votes statewide.
Democrats in the state are looking to replicate the political coalition of Senator Tammy Baldwin, the Democrat who won in 2018 by energizing her party’s constituencies while limiting losses in the suburbs and rural regions.
In an interview on Election Day, Ms. Baldwin said she believed Mr. Biden would be successful.
“They figured out a way to be here virtually, even if they weren’t here in person,” she said. “We’ve learned a lot of lessons about how we conducted 2016, from the party all the way on down.”
There are several reasons Democrats remain confident in Wisconsin. The state saw increased turnout in Madison, reaching more than 80 percent, according to election officials. In Milwaukee, another of the state’s liberal strongholds, turnout seemed better than four years ago but below the expectations of the state’s left wing.
Mr. Biden built a political campaign focused on Midwestern voters, aimed at clawing back many of the ideological moderates who voted for Mr. Trump in 2016. For all the talk about winning states like Florida, Iowa or Texas, Democrats in Wisconsin say the campaign will be decided as it began — with Mr. Biden betting his political future on the region of the country that he is most associated with.
Though a glance at the top-line numbers appeared to show Michigan largely accounted for and trending toward Mr. Trump, some of the state’s major population centers had hundreds of thousands of ballots yet to be counted as of early Wednesday. And these could easily tip the state to Mr. Biden, as Democrats have said they expect.
Polls taken before the election showed the former vice president considerably ahead, outside the margin of error.
Mr. Trump’s lead so far reflects his advantage in the Election Day vote — not the early vote, which is a larger share of the overall ballots cast in the state and favors Mr. Biden.
In Detroit, the city clerk had counted only about half of what was expected. The clerk’s office reported having 125,000 votes tallied just after 2 a.m.
For comparison purposes, Detroiters cast 248,000 ballots in 2016, when turnout was low. This year, election officials have said they expect turnout to easily surpass that, potentially exceeding 2008 and 2012 when President Barack Obama was on the ballot.
Mr. Biden is expected to easily get 90 percent of the vote in Detroit.
In Michigan’s bellwether Macomb County, which voted twice for Mr. Obama and then for Mr. Trump in 2016, the president was ahead because of a large advantage with voters who went to the polls on Tuesday. But only around half of the precincts had fully counted their early and Election Day ballots, leaving Mr. Biden considerable opportunity to close that gap.
And in Oakland County, the state’s second-largest, what began as a significant lead for Mr. Trump Tuesday evening vanished into an advantage for Mr. Biden by Wednesday as more and more precincts reported their early votes.
Democrats have won Oakland County in every recent presidential election. Hillary Clinton carried it by eight points in 2016, and Mr. Biden appeared on track to surpass that margin of victory.