Hillary Clinton sought Monday to cement her lead over Republican White House rival Donald Trump, looking to conquer swing states including Florida and Ohio where early voting has already begun.
With barely two weeks before Election Day, Clinton and Trump are blitzing the nation's crucial battlegrounds where the race will be won or lost November 8.
But voters in Chicago, Charlotte, Miami, Cleveland and Las Vegas are already going to polling stations to cast ballots -- with initial indications suggesting a surge in early voting among Clinton's Democrats.
No less than 37 of the 50 states provide in-person voting in advance of the big day, and all offer some form of absentee ballots by mail.
"We've got to get people turning out. That's the most important thing we can do," Clinton said Monday on WZAK radio station in Cleveland.
In 2012, fully a third of all ballots were cast in advance, according to the Census Bureau. The Clinton campaign is counting on an even larger early turnout this year, as it expands its efforts to mobilize committed and undecided voters alike, particularly in swing states Florida, Nevada and North Carolina.
"It is possible, because there is so much access to early voting, that we could build an insurmountable lead in those keys states before election day," Clinton campaign manager Robby Mook said this month.
Some six million Americans have already voted, according to election expert and University of Florida professor Michael McDonald.
"Nothing can go wrong now. My vote's in," Hannah Widlus, 61, told AFP after casting her ballot for Clinton at a Chicago polling station crowded with morning voters.
Normally she would not vote early, but Widlus said she was eager to do so in part because of "the circumstances of the current election," which she said "has been made a mockery of this year."
Early ballots are not counted until Election Day, but a look at who is requesting or casting them shows gains for Clinton, particularly in Nevada, where her ground game is prodigious, and in Florida, where Republicans usually dominate early voting.
"At a comparable time in 2012, registered Republicans had a lead of 5.3 percentage points over Democrats in returned mail ballots" in Florida, McDonald wrote in Monday's Huffington Post.
"As of Saturday, the Republican lead was 1.6 percentage points."
Campaigning for Clinton in Las Vegas at the weekend, President Barack Obama drove the advance voting message home: "Everybody has got to vote early," he said. "That's how we won in '08. That's how we won in 2012. That's how we're going to win in 2016."
Most polls put Trump a few points behind Clinton in Florida. Trump was hosting two rallies in the state Monday, while Clinton campaigns there on Tuesday and then Wednesday, her 69th birthday.
"The truth is I think we're winning," Trump said at a farmers' roundtable in Boynton Beach, Florida, adding he believed he was ahead in Ohio and Iowa.
"We're doing great in North Carolina," and "I think we're doing great in Florida, I think we're going to win Florida big."
Trump's campaign manager Kellyanne Conway appeared to contradict her candidate, admitting Sunday on NBC's "Meet the Press" that "we are behind," but nevertheless insisting that the race was not over.
"We're not giving up. We know we can win this," she added.
Clinton, the former secretary of state vying to become America's first female president, leads the Republican real estate mogul nationally by about six points according to the RealClearPolitics average of polls. She also leads in most battleground states.
A new national ABC News poll showed her leading by 50 percent to 38 percent -- her highest score since the race to succeed Obama began.
Conscious that winning the minority vote will help lead her to victory, Clinton meanwhile campaigned Sunday at a mainly black church in Durham, North Carolina.
Obama narrowly won the southeastern state in 2008, but lost it to Mitt Romney four years later.
Clinton is now pulling out all the stops to try and win it back, returning there Thursday with potent surrogate Michelle Obama. It will be the first joint rally for the former and current first ladies.