More than 91 million Americans have already cast their votes in the presidential election and millions more are expected to vote on Tuesday, with some predicting turnout of over 60 percent.
A majority of states have reported record early voter turnout and several have broken their records for voter registration. Nationally, votes already cast account for 43 percent of registered voters, according to CNN.
Democrats, in particular the party's presidential candidate Joe Biden, look set to be bigger beneficiaries of these voting dynamics overall than the Republicans and President Donald Trump.
"The early vote appears to confirm the polls that there has been a swing to the Democrats since 2016, which should benefit Biden," Michael McDonald, a professor at the University of Florida who specializes in American elections, wrote on his website.
"But, the swing is not uniform, and some of the closest states in 2016—Florida and North Carolina—appear to be close again."
The outcome of the election will be decided in key swing states and the crucial counties within them. In 2016, Trump won the White House with narrow victories in Michigan, Pennsylvania, and Wisconsin.
All three states allow voters to register in person on November 3, so it's not yet possible to have a complete picture, but registration and early voting numbers show a trend toward high turnout on Tuesday.
This may be crucial in critical counties that swung Michigan, Pennsylvania, and Wisconsin four years ago. Trump won by less than one percent in each state.
McDonald, who runs the U.S. Elections Project, wrote that it "appears likely that around 100 million early votes will be cast by the time Tuesday morning reports are processed."
He predicts a record turnout: "Examining each state in turn, and rolling up the state estimates to a national estimate, I arrive at a total turnout rate of 160.2 million votes, or a turnout rate for those eligible to vote of 67.0 percent."
More than 2.6 million ballots have already been cast in Michigan, Detroit's Metro Times reported. This represents more than a third of registered voters in the state.
Election pundits will be paying particular attention to Macomb County, which went for Trump in 2016 after voting for President Barack Obama twice. It's Michigan's third-largest county and has gone for the statewide winner in the last seven elections.
Pennsylvania is considered essential to Trump's re-election and Biden enjoys the narrowest lead there of the thee former "Blue Wall" states. The state has seen record early voter turnout, while Democrats have maintained their edge in voter registrations.
There are 700,000 more registered Democrats than Republicans in Pennsylvania, but the election will likely be decided in places like Luzerne and Erie Counties, both of which backed Trump in 2016 after twice voting for Obama.
Luzerne County has seen an increase in registered Republicans, adding 9,081 registered voters in the past four years.
However, there are still more registered Democrats in the county, despite a decline of 3,097 voters. There are 104,958 registered Democrats compared to 83,197 Republicans, according to the Pennsylvania Department of State Figures.
Democrats in Erie County feel more confident this year than in 2016, according to Go Erie, but the local Republican Party has seen registrations rise 10.5 percent in the past four years compared to a rise of just 1.5 percent for local Democrats.
However, registered Democrats outnumber Republicans there by 25,500. Erie County is considered a bellwether.
Results in Pennsylvania will also be driven by turnout in Chester and Philadelphia Counties, which voted for Clinton in 2016. If Biden can increase the Democratic vote there, it may go a long way to counteracting the Trump vote in other parts of the state.
The Trump campaign will also be hoping to increase their share of the vote in Westmoreland County.
In Wisconsin, half of all registered voters have already cast ballots, the state's Elections Commission reported on Sunday. Some 1,873,403 have voted, representing 50.8 percent of registered voters there, while 100,922 people registered to vote in October. Wisconsin doesn't record voters' party affiliation.
Grant County voted for Trump in 2016 and Obama in 2012 and 2008 and is seen as one of Wisconsin's "swingiest" counties, according to the New York Times.
Brown County voted for Obama in 2008 but opted for the Republican candidate in subsequent elections. More than 11,000 ballots have already been cast there.
Results in Grant and Brown Counties could be an indication of where the state will go, though high turnout for Biden in Dane County could offset Trump's support elsewhere. Dane County has already seen 72 percent of the total number of votes cast in 2016, Politico reported.
Trump's path to victory also runs through Florida, which he won in 2016 but where Biden enjoys a narrow lead, according to poll tracker FiveThirtyEight. The state has already passed the halfway mark for ballots cast in 2016. Trump won Florida by 1.2 percent.
Michael McDonald notes that Florida "looks darn close" and estimates that 75 percent of votes in the state will be cast early unless there's "astronomical turnout unlike anything ever seen before in any state in modern times" on Tuesday.
Three counties with different voting histories—Pinellas, Miami-Dade, and Osceola—may be crucial in securing a win there.
Pinellas County went narrowly for Trump in 2016 after twice voting for Obama, while Miami-Dade and Osceola Counties have been more reliably Democratic and high turnout there would help Biden.
Miami-Dade County passed its 2016 early voting total on October 31, with 478,000 votes cast per the Miami Herald.
Pinellas County was reportedly lagging behind other Florida counties in early voting last week, likely because the county has just five early voting locations, but it had seen almost 55 percent turnout by October 29, some 400,000 votes, WFTS reported.
Early voting totals in Osceola County reached 137,436 on November 1, while 141,468 votes were cast for president in 2016, Florida election data shows.
Four states—Florida, Michigan, Pennsylvania, and Wisconsin—could decide the next president of the United States.
While Biden is leading in polls in all four, voter registration, early voting, and turnout on Tuesday in just a handful of counties could determine the results.
