Republican candidate Donald Trump has said he is going to target states seen as Democratic strongholds in the last two days before the US election.
He will visit Pennsylvania, Michigan and also Minnesota, which has not gone Republican since 1972.
He started off a four-state swing on Saturday in Florida, where rival Hillary Clinton also campaigned.
She unveiled an advert to run in nearly a dozen states, set to the Katy Perry song, Roar.
Perry will appear with Mrs Clinton later on Saturday at a rally in Philadelphia, Pennsylvania.
Opinion polls suggest Mrs Clinton is still ahead in key states.
But she has seen her lead slip following last week's FBI announcement that it was looking into emails that may be connected to her use of a private email server while she was secretary of state.
A nationwide McClatchy-Marist opinion poll on Saturday gave her a one point lead, compared to six in September.
A YouGov polling estimate on Saturday gave her a three-point lead.
Some 37 million early voters have already cast their ballots. Reports suggest many more Latino voters are turning out early in key states including Florida, Arizona and Nevada compared to past elections.
Analysts in Nevada say the Democrats appear to have taken a significant lead there because of the early ballots.
'Repeal Obamacare'
Donald Trump told a rally in Tampa, Florida: "We're going into what they used to call Democrat strongholds, where we're now either tied or leading. We're going to Minnesota, which traditionally has not been Republican at all."
Pennsylvania and Michigan are also both on his agenda and they too have been tough states for Republicans. They have not won them since 1988.
After Tampa, Mr Trump headed to Wilmington in North Carolina, where he was introduced by his wife, Melania.
Mr Trump turned his fire on the Affordable Care Act, also known as Obamacare.
"Real change begins with immediately repealing and replacing Obamacare," he said.
Mrs Clinton addressed a rally in a hoarse voice in Pembroke Pines in Florida, telling supporters: "I don't think I need to tell you all of the wrong things about Donald Trump", before cutting the speech short amid a downpour of rain.
Florida is a massively important state, particularly for Mr Trump, with many seeing it as a must-win. Candidates need 270 electoral college votes to win the presidency. Florida is worth 29.
The contest appears to be tight. Real Clear Politics' poll average puts the Democratic candidate ahead, but poll analysis website FiveThirtyEight says Mr Trump has a 52.6% chance of winning the state.
Mrs Clinton's campaign has revealed she will do a two-minute national TV commercial on Monday night which they expect will reach a combined audience of 20 million people.
She has been relying heavily on A-list supporters - on Friday in Cleveland it was singer Beyonce and rapper husband Jay Z.
After Katy Perry, she will take the stage with basketball star LeBron James in Cleveland on Sunday.