WASHINGTON- In a final burst of campaigning, US President Donald Trump and his Democratic challenger Joe Biden have criss-crossed Midwestern states that may hold the keys to the White House.
Mr Biden went on the offensive in Iowa, a state that voted for Mr Trump by 10 points in 2016.
Mr Trump made a play for Minnesota, which voted narrowly for Hillary Clinton four years ago.
Mr Biden holds a solid national lead ahead of Tuesday's general election.
But his advantage over Mr Trump is narrower in the handful of US states that could vote for either candidate and ultimately decide the outcome in four days' time.
More than 85 million people have voted early, 55 million of them by post, setting the US on course for its biggest voter turnout in over a century.
The Democrat has taken a more measured pace to campaigning than his rival, spending much of the election cycle at his home in Wilmington, Delaware, citing coronavirus restrictions.
But on Friday he sprinted through Iowa, Wisconsin and Minnesota on his busiest day yet.
When Mr Biden was last in Iowa, in January, his presidential campaign was in serious jeopardy after he was defeated in a party vote to choose the Democratic challenger to Mr Trump.
Now Mr Biden could be days away from becoming the 46th president of the United States.
He made a 22-minute appearance at a drive-in event in a car park outside the Minnesota State Fairgrounds.
But a throng of Trump supporters turned up and tried to drown him out by honking their horns during his speech.
"These guys are not very polite, but they're like Trump," Mr Biden said.
He was interrupted again later in the speech while urging a national mask-wearing mandate to counter coronavirus.
"This isn't a political statement like those ugly folks over there beeping their horns," Mr Biden snapped, eliciting a renewed cacophony of vehicular horns.
The Democrat used many well-honed attack lines on his rival, saying: "Donald Trump has waved the white flag and surrendered to this virus but the American people don't give up, they don't cower and neither will I."
He also added a local pitch to the state's Somali diaspora.
"That's why he [Mr Trump] shamelessly equates Somali refugees, folks seeking a better life in America, contributing to this state and our country, with terrorists." He added: "We need a president who will bring us together, not pull us apart."
Mr Biden's visit to Minnesota, where he holds a steady lead in opinion polls, was interpreted by some election-watchers as a sign that the Democrat's campaign was anxious about the state.
The candidate told reporters in Delaware as he set out for the Midwest: "I don't take anything for granted."
His campaign war chest, double the size of Mr Trump's, has earned him the luxury of making a play for conservative states such as Iowa and Georgia, where a Democrat has not won the presidency since Bill Clinton in 1992. (BBC)