Hillary Clinton urged voters in Iowa to start casting ballots on Thursday, more than five weeks before Election Day.
Mrs Clinton's 10-city tour of Iowa brought the Democratic presidential nominee back to a state where she eked out a win in the caucuses over Bernie Sanders.
With her focus now on defeating Donald Trump, she was hoping that putting an emphasis on early voting could help her replicate President Barack Obama's successful strategy in the battleground state four years ago.
In Des Moines, Mrs Clinton planned a speech focused on childcare challenges faced by middle-class families.
It is a traditionally Democratic issue that Mr Trump has taken on recently, prompted largely by interest from his daughter, Ivanka.
The Republican nominee was holding a rally in New Hampshire on Thursday, a day after Mrs Clinton campaigned there with Mr Sanders in an appeal to young voters.
While Mrs Clinton sought to broaden her appeal to voters still on the fence, Mr Trump was sticking with his strategy of focusing on the loyal base of working-class voters whose enthusiasm has driven his campaign.
Mr Trump has brushed off harsh critiques of his performance in the first presidential debate that have come from supporters and opponents alike.
However, in a nod to the concerns expressed by some Trump allies that he was insufficiently prepared, his campaign and the Republican National Committee released a "TRUMP Debate Preparation Survey" ahead of his second showdown with Mrs Clinton.
The survey, a gimmick intended to engage supporters online, asks whether Mr Trump should use the second debate to criticise Mrs Clinton for her policies on terrorism, economics and trade - questions sure to elicit an enthusiastic "yes" from Trump backers.
Absent was any inquiry about whether Mr Trump should bring up former president Bill Clinton's infidelities, as he has repeatedly threatened to do.
In another reminder of how far this year's presidential campaign has veered into baffling territory, third-party candidate Gary Johnson was being ridiculed after he was unable, in a television appearance, to name a single world leader he admired.
The awkward moment drew immediate comparisons - including by Mr Johnson himself - to his "Aleppo moment" from earlier in the month when he did not recognise the besieged city in Syria.
"I'm having a brain freeze," Mr Johnson said on Wednesday.
Mr Trump was also facing fresh questions on Thursday about business opportunities he explored in the late 1990s in Cuba, apparently in violation of the US embargo on the communist island.
The work was done by a consulting firm called Seven Arrows on behalf Trump Hotels & Casino Resorts Inc, Mr Trump's publicly traded casino company, Newsweek reported.
The magazine said Mr Trump reimbursed the consulting firm for 68,000 US dollars of business expenses for its Cuba work - even though neither Mr Trump nor the firm had sought a federal government waiver that would have allowed them to pursue such activities.
Mrs Clinton's focus on early voting reflected the premium that Democrats are placing this year on trying to get their voters to turn out - if possible, long before November 8.
Although the political map favours Mrs Clinton this year, Democrats are concerned that a lack of enthusiasm will keep their voters from showing up in the same numbers that led to Mr Obama's victories in the last two elections.
More than four in 10 Iowa voters cast early ballots in 2012, and Mrs Clinton's campaign is hoping that even higher interest in early voting this year will give her a decisive edge.
Early voting - either by mail or with voting booths that are open before election day - has been on the rise in the United States.
It is a way to increase voter turnout, especially for Americans who have difficulties making it to the polls on November 8.
Other states have already begun in-person early voting, but Iowa is getting attention because it is the first battleground state to do so.
That means it is among a dozen states that are not reliably Democratic or Republican, so can sway the outcome in the state-by-state presidential vote.
For Mrs Clinton, the early voting strategy is key to any prospects she may have for pulling off victories in states like Arizona and Georgia.
Both states traditionally vote Republican in presidential races, but Democrats hope that the growing Hispanic populations and Mr Trump's unpopularity could alter the calculus this year.
Mrs Clinton's running mate, Tim Kaine, was hunkered down in North Carolina for three days of preparations ahead of Tuesday's vice presidential debate.
He told reporters in Raleigh that he had been studying the first Clinton-Trump debate and practising against a dramatised version of Trump running mate Mike Pence, played in prep sessions by Washington lawyer Bob Barnett.