Hillary Clinton campaigns Thursday in Iowa just as the state begins early voting, with the Democrat seeking to pry the pivotal swing state away from Republican Donald Trump and spur turnout that could ultimately decide the presidency.

The businessman-turned-populist stumped in Iowa a day earlier, appealing to white, blue-collar workers who have helped push him into the lead in the "Buckeye" state, where the latest polls put him up nearly five points.

Iowa has long been an essential staging post on the path to the White House.

Barack Obama's primary win in Iowa in 2008 propelled him to a thumping presidential victory that year and in 2012 that all but secured his re-election.

But Clinton has seen a decade-long Democratic advantage reversed.

Her swing there coincides with the launch Thursday of non-postal early voting, which both campaigns see as a potentially critical opportunity for voters to cast ballots in person over the next several weeks ahead of Election Day.

"In 2012, more than four in 10 voters cast their ballots early in Iowa, allowing the Obama campaign to know the outcome of that state days before election day," said a Clinton campaign aide.

Locking down votes now could help the campaign tailor time and resources as the election enters the final stretch.

"Early (voting) is a critical component of our organizing effort in all the battleground states," the Clinton aide added.

"In Nevada and North Carolina, more than half of the state's voters cast their ballot early."

More vitally for Clinton will be to ensure that chunks of the electorate actually turn out to vote and reverse Trump's lead.

Trump is most likely to win if the coalition of young, African American and Latino voters who voted for Obama decide to stay at home on November 8.

Clinton's main tool to inoculate against that possibility is likely to be Trump himself.

Her campaign has framed the election as an existential moment for the republic, a choice between Clinton's safe pair of hands and the latent authoritarianism of an erratic mogul.

Clinton hammered away at Trump's propensity to stretch the truth, as it released an online video highlighting several moments during the pair's first debate this week when Clinton pointed to statements Trump had made in the past, only to have Trump insist he never made them despite clear evidence.

"Donald Trump may lie, but the tape doesn't," Clinton tweeted Thursday.

After a day on the back foot, Trump resumed his attacks on his rival during a stopover in Council Bluffs, Iowa, painting her as a pawn of special interests.

"Hillary Clinton is an insider, fighting for her donors and her insiders and mostly fighting for herself," Trump said.

"I am an outsider fighting for you. We're fighting together."

He also alluded to Iowa's early voting, and called on his supporters to demand that they and their friends "get out of bed" to go vote.

"You have no choice. You have to campaign on the streets, spread the love that we have in this room," Trump said.

"We have to get out there folks, otherwise this movement will be wonderful to read about someday."

The brash billionaire was due to hold a rally later Thursday in New Hampshire, criss-crossing with Clinton who campaigned in the small but crucial state Wednesday.

After a pneumonia and a debate-induced break that were tough for her campaign, Clinton was back on the trail, brimming with renewed confidence after experts widely declared her the winner of her showdown with Trump.

On Wednesday, she appeared with one-time Democratic rival Bernie Sanders, whose improbable journey from low-profile socialist senator to serious presidential contender was made possible by enthusiasm among young voters.

"This election is enormously important for the future of our country," Sanders, 75, told the New Hampshire rally. "It is imperative that we elect Hillary Clinton as our next president."

The latest Quinnipiac poll showed Clinton at just 31 percent among young voters, an uncomfortably small lead over Trump's 26 percent.

Third-party Libertarian candidate Gary Johnson jumped from 16 percent in August to 29 percent in September -- prompting hand-wringing among the Democrats less than six weeks before the election.