The FBI is monitoring criminal threats to election workers and infrastructure from a 24/7 command post set up to ensure the election is safe and secure.

The command post, which is staffed with 80 people from more than a dozen agencies, will continue to operate for at least nine days.

"This command post is an opportunity for us to bring people together, all the different subject matter experts here in the FBI at headquarters and in the field, and we bring in our partners so the intelligence and threats that come in, and we can disseminate that information to the key partners, which is state and local officials around the United States," said Jim Barnacle, deputy assistant director of the FBI's Criminal Investigative Division.

The FBI is focused on criminal threats, such as threats to election workers, foreign malign influence, cyberthreats and acts of violence.

-ABC News' Luke Barr

As millions of Americans descend on polling locations across the country, election officials and law enforcement authorities are focused on administering a fair and safe election under a cloud of threats, online disinformation, and the potential for a grueling legal fight in the weeks ahead.

Although a typical Election Day inevitably includes some hiccups like long lines or weather-related issues, this year election workers face the additional challenge of a heightened threat environment and an onslaught of litigation concerning voting rules and ballot counting.

Even so, election officials on Monday expressed confidence in their ability to execute on Election Day. Pennsylvania Secretary of State Al Schmidt said the vote in his state would be "free, fair, safe, and secure." Georgia Secretary of State Brad Raffensperger said that "at the end of the day, it's going to be fair and fast and accurate."

And in North Carolina, Karen Brinson Bell, the executive director of the state's Board of Elections, said, "Despite all the naysayers, despite all false information and sensationalist rhetoric out there about elections, and despite a devastating hurricane, we are making this happen in North Carolina."

-Lucien Bruggeman

Former President Donald Trump used his final campaign rally in Grand Rapids, Michigan, to attack high profile Democrats including President Joe Biden and former Speaker of the House Nancy Pelosi.

Trump told attendees he is "not running" solely against Vice President Kamala Harris. "I'm running against an evil Democrat system," he said. "These are evil people."

Trump launched into attacks on Biden, pushing unfounded claims that Harris only became the nominee because Democrats wanted to be "politically correct."

Trump then made fun of Harris's name calling it "a strange name," before pivoting back to criticize Biden.

"I wasn't running against Biden either," Trump said. "He was stuck in a basement. I didn't even run against him. Now running against a very evil system, and we have to defeat that system, and America's future will be an absolutely incredible one."

The former president also mouthed an expletive when referring to Pelosi. "She's a crooked person," he added. "She's a bad person, evil."

-ABC News' Lalee Ibssa, Soo Rin Kim and Kelsey Walsh

Former President Donald Trump's final campaign rally in Grand Rapids, Michigan, saw the Republican presidential nominee urging supporters to head to the polls while also again casting doubt on the security of the electoral process.

Multiple times throughout Trump's speech he told supporters to go out to the polls "tomorrow." However, given the rally was happening after midnight, people in the crowd started yelling "today" and then Trump falsely said the election was happening on Wednesday.

"It sounds so much better when you say tomorrow, Wednesday," Trump said. "But that's okay. I want to be exactly accurate for them, but go out today and vote. And I guess seven o'clock or whatever, whatever time it is, doesn't matter, and we're going to have the greatest victory in the history of our country."

Trump then suggested that his supporters might be to blame if he does not defeat Vice President Kamala Harris.

"There's nothing they can do" if Republicans turn out, Trump said of his opponents. "In other words, to make you feel a little guilty, we would only have you to blame." Later, Trump claimed he has the "silent majority" and urged his supporters to "speak up."

The former president also again cast doubt on the security of voting machines, despite officials and experts confirming the security of the election system.

"Perhaps I will be president in less than 24 hours, or maybe it will take these machines that we pay so much for two weeks," Trump said, claiming that paper ballots would be cheaper, faster and more secure.

"What the hell is happening in the inside of those machines?" he continued. "If you wait, we want the answer tomorrow, tonight," Trump said, quickly correcting himself. "We want the answer tonight."

"You have to cheat," Trump said about Democrats. "Who the hell is going to approve that stuff? Who's going to prove open borders with criminals pouring into our country by the millions now they have to cheat. They have to cheat, and they do, and they do it very well, actually."

-ABC News' Lalee Ibssa, Soo Rin Kim and Kelsey Walsh