Millions of Americans have flocked to the polls amid a deadly pandemic in a mostly calm, orderly show of political determination and civic duty that belies deep tensions shaping one of the most polarising presidential races in US history.
The masks worn by many voters and the sight of boarded-up storefronts in major city centres were reminders of two transformative issues defining the 2020 election, with COVID-19 still ravaging parts of the country after a summer of mass protests against racial injustice.
The FBI and the New York attorney general's office opened investigations into torrents of anonymous robocalls urging people in several states to stay home.
A Republican congressional candidate in Pennsylvania on Tuesday sued election officials in a suburban Philadelphia county, accusing them of illegally counting mail-in ballots early and giving voters who submitted defective ballots a chance to re-vote.
And a federal judge ordered the US Postal Service to conduct a sweep of some facilities across the country for undelivered mail-in ballots and to ship them immediately to election offices to be counted.
But few if any major disruptions were reported at polling sites through the day as civil liberties groups and law enforcement were on high alert for any interference.
In New York City, some voting lines snaked around blocks, but in many places, from Los Angeles to Detroit and Atlanta, lines were short or non-existent.
Poll workers surmised this was due to an unprecedented wave of early voting. More than 100 million ballots were cast before Election Day, a new record.
"I lost my absentee ballot, and I'm not going to miss this vote," said Ginnie House, 22, an actor and creative writing student who flew back to Atlanta from New York just to cast her vote for Biden.
Across the partisan divide was Linda King, 73, an education coordinator for a nonprofit, arrived early to cast her ballot for Trump at a church in Champion, Ohio, but found the parking lot jammed and decided to return in the afternoon.
"I had never seen anything like that," she recounted. King said she was determined to vote in person on Election Day out of sheer habit.
The US Justice Department's Civil Rights Division said it deployed personnel to 18 states to watch for voter intimidation and suppression. And a senior US Department of Homeland Security official told reporters on a conference call there was no evidence of violence at polling stations during the day.
Business owners in cities across the country boarded up street-level windows for fear that civil unrest could erupt later, especially if the election's outcome were delayed.
Disputing Trump's assertions that continuing to count votes after Election Day was open to abuse and somehow "dangerous," Ohio Secretary of State Frank LaRose, a Republican, told reporters on Tuesday it was normal for ballots to be tabulated days after polls closed.
Irregularities at the polls were isolated. A man legally carrying an unconcealed firearm was arrested and charged with trespassing at a polling site in Charlotte, North Carolina.