PITTSBURGH — Closing out a campaign shadowed by a once-in-a-century pandemic, President Donald Trump charged across the nation Monday, delivering without evidence his incendiary allegation that the election is rigged, while Democratic challenger Joe Biden pushed into states once seen as safely Republican, looking to secure his path to the White House.

America stood at a crossroads. Never before in modern history have voters faced a choice between candidates offering such opposite visions as the nation confronts a virus that has killed 230,000 Americans, the starkest economic contraction since the Great Depression and a citizenry divided on cultural and racial issues.

The two men also broke sharply Monday on the voting process itself while campaigning in the most fiercely contested battleground, Pennsylvania.

The president threatened legal action to stop counting beyond Election Day. If Pennsylvania ballot counting takes several days, as is allowed, Trump charged that “cheating can happen like you have never seen.”

Biden, in Pittsburgh, pushed a voting rights message to a mostly Black audience, declaring that Trump believes “only wealthy folks should vote” and describing COVID-19 as a “mass casualty event for Black Americans.”

“We’re done with the chaos, we’re done with the tweets, the anger, the hate, the failure, the irresponsibility,” said Biden, whose campaign has focused on increasing turnout by Black voters, who could prove the difference in several battleground states.

Both campaigns insist they have a pathway to victory, though Biden’s options for winning the required 270 Electoral College votes are more plentiful. Trump is banking on a surge of enthusiasm from his most loyal supporters in addition to potential legal maneuvers.

Trump spent the final full campaign day sprinting through five rallies, from North Carolina to Pennsylvania to Wisconsin. Biden devoted most of his time to Pennsylvania, where a win would leave Trump with an exceedingly narrow path. He also dipped into Ohio, a show of confidence in a state that Trump won by 8 percentage points four years ago.

The two men delivered their final messages, with Biden emphasizing the pandemic. He declared that “the first step to beating the virus is beating Donald Trump,” and he promised he would retain the nation’s leading infectious disease expert, Dr. Anthony Fauci, whom the president has talked of firing.

Trump, meanwhile, made only passing mention of what his aides believe are his signature accomplishments — the nation’s economic rebound, the recent installation of Supreme Court Justice Amy Coney Barrett — in favor of a torrent of grievance and combativeness. He angrily decried the media’s coverage of the campaign while complaining that he also was being treated unfairly by, in no particular order, China, the Electoral College system and rock singer Jon Bon Jovi.

“I have been under siege illegally for three-and-a-half years. I wonder what it would be like if we didn’t have all of this horrible stuff. We’d have a very, very calm situation,” said Trump at an evening rally in Michigan. “People see that we fight and I’m fighting for you. I’m fighting to survive. You have to survive.”