Joe Biden moved his campaign train to Pennsylvania and Ohio, as Mr Trump toured the voting battlegrounds of Wisconsin, Michigan, North Carolina, and Pennsylvania.
National polls showcase Biden having a firm lead in Tuesday’s election.
But his lead is slimmer in a number of states that could decide the result.
Almost 99 million people have already cast their ballots in early voting, putting the country on course for its highest turnout in a century.
For a president to be elected, a candidate must amass at least 270 votes in what is called the electoral college. Each US state gets a certain number of votes partly based on its population and there are a total of 538 up for grabs.
This system explains why it is possible for a candidate to win the most votes nationally – as Hillary Clinton did in 2016 – but still lose the election.
Tuesday’s vote comes amid the ongoing coronavirus pandemic. The US has recorded more cases and more deaths than any other country worldwide, reporting more than 81,000 new infections on Sunday alone.
As the nation counts down the hours to the vote, there are fears that pockets of post-election violence could break out. Businesses in the nation’s capital, Washington DC, and in New York City have been seen boarding up their premises due to concerns about unrest.
After a punishing schedule of rallies in six states on Sunday, President Trump sprinted through four more battleground states on Monday.
In North Carolina, he told supporters that “next year will be the greatest economic year in the history of our country”. The rally was postponed from Thursday due to Hurricane Zeta.
He touted numbers that he says “nobody even thought possible”.
The US economy saw record-breaking 33% growth in the third financial quarter of this year, following a record 31% contraction in the second. Economists warn the damage inflicted by the pandemic – the biggest decline in the US economy in more than 80 years – could still take years to overcome.
After North Carolina, Mr Trump headed to Scranton, Pennsylvania, the city where his opponent lived until he was 10. At a rally there he reminded his supporters that he won the state in 2016 despite polls suggesting he would lose.