Polling stations in the key battleground state of Florida have opened for early voting, where Hillary Clinton and Donald Trump remain in a tight race.
The Republican candidate Mr Trump is blitzing the state with five rallies while Democrat Mrs Clinton is also swinging through the Sunshine State.
Early voting by mail began in Florida weeks ago and over 1,000,000 people have already cast their votes.
Mrs Clinton, the Democratic candidate, holds a narrow three-point lead according to a new CBS/YouGov poll.
The former secretary of state had 46 percent of the vote compared with Mr Trump's 43 percent, the poll found.
Mr Trump, who spent the weekend in Florida, is slated to appear at more campaign stops across the state before heading to North Carolina on Tuesday.
"We are going to win the great state of Florida and we are going to win back the White House," Mr Trump said at a rally on Sunday in Naples.
But recent polls have put Mrs Clinton well ahead of her rival, both nationally and in several battleground states.
Polling in Republican strongholds including Arizona, Georgia and Utah have also shown closer-than-expected races.
President Barack Obama was quick to point out Mr Trump's flailing support among Republicans when he lashed out at Darrel Issa at a fundraiser for his Democratic opponent Doug Appelgate late on Sunday.
The president rebuked Mr Issa for fanning the flames that led to Mr Trump's nomination, calling him "Trump before Trump".
He also called Mr Issa "shameless" for sending out campaign brochures "touting his cooperation on issues" with the White House after years of critcising Mr Obama.
Meanwhile, Mr Trump dismissed surveys on Sunday, urging supporters to help him prove that polls were wrong.
"I'll tell you what, we're doing well in the polls. But, you know, I really think those polls are very inaccurate when it comes to women. I think we're doing better with women than with men, frankly," he said.
He also mentioned what he would do as president during his first 100 days in office, which included repealing the Affordable Care Act, lowering taxes and enacting his immigration plan.
He said he would support mandatory minimum prison sentences for anyone who attempts to illegally re-enter the US after being deported.
With less than two weeks before election day, Mr Trump's campaign has admitted to being "behind" but added it was not giving up.
What happens next?
- The two candidates will spend the remaining 15 days before the election criss-crossing the country in their bid to persuade undecided voters. Expect to see lots of appearances in battleground states such as Ohio, North Carolina, Florida and Pennsylvania.
- Voters will go to the polls on Tuesday 8 November to decide who becomes the 45th president of the US.
- The new president will be inaugurated on 20 January 2017.
Trump wins first major newspaper endorsement
Despite his slip in the polls, the Republican candidate received his first major newspaper endorsement on Sunday from Nevada's largest newspaper, The Las Vegas Review-Journal.
The newspaper, which is owned by casino mogul and Republican Trump supporter Sheldon Adelson, acknowledged Mr Trump's flaws but suggested he would disrupt Washington's political norms.
"Mr Trump represents neither the danger his critics claim nor the magic elixir many of his supporters crave," the endorsement said.
"But he promises to be a source of disruption and discomfort to the privileged, back-scratching political elites for whom the nation's strength and solvency have become subservient to power's pursuit and preservation."
Several newspapers broke with longstanding traditions of backing Republicans or abstaining from presidential endorsements altogether to support Mrs Clinton, with many noting a marked stance against Mr Trump.