Democratic presidential candidate Kamala Harris and her Republican rival, Donald Trump, delivered radically different messages on the U.S. campaign trail on Monday as they sought to win over undecided voters in the two weeks before Election Day.

Vice President Harris, campaigning alongside former Republican lawmaker Liz Cheney, argued that Trump, the former president, was a threat to democracy.

As the election draws closer, Harris has been sharpening her attacks on Trump's fitness for office, often calling him "unstable" or "unhinged" and questioning his temperament.

"In many, many ways Donald Trump is an unserious man, but the consequences of him being president of the United States are brutally serious," Harris, 60, said at an event in Malvern in Pennsylvania, one of seven battleground states expected to decide the winner of the Nov 5 election.

Trump, 78, frequently rejects any notion that he is a threat to democracy, arguing that it is Democrats who are the real threat because of the criminal investigations he and his allies have faced for their attempts to overturn his 2020 election loss.

Trump crisscrossed North Carolina on Monday to gin up support in the ultra-competitive state. At one stop in the hurricane-battered mountains, he urged supporters to go to the polls despite the hardships they were facing.

While Harris was suggesting Trump was unfit for office, the former president was questioning the Biden administration's competence.

Trump renewed his criticisms of the emergency management agency FEMA and sought to relate to working-class supporters by praising his nonstop efforts on his own behalf.

"I've done 52 days without a day off, which a lot of these people would respect," Trump said at a lectern backed by rubble from massive floods that hit the area last month.

With opinion polls showing a close race, the two candidates are picking up the pace, their frenzied campaign schedules underlining the importance of small pockets of voters that could put either candidate over the top.

At an event with Harris in Royal Oak, Michigan, Cheney sought to give Republicans who are on the fence permission to support the Democrat without worry of reprisal.

"I certainly have many Republicans who will say to me, 'I can't be public.' They do worry about a whole range of things, including violence, but they'll do the right thing," Cheney said. "And I would just remind people, if you're at all concerned, you can vote your conscience and not ever have to say a word to anybody."

Cheney and her father Dick Cheney, who was vice president under President George W. Bush and is still vilified by many Democrats for his bullish defense of the U.S. invasion of Iraq, are staunch conservatives and two of the most prominent Republicans to have endorsed Harris.

In a post on his Truth Social platform on Monday, Trump called Liz Cheney "dumb as a rock" and a "war hawk." He accused her of wanting to go to war with "every Muslim country known to mankind" just like her father, who he called "the man that ridiculously pushed Bush to go to war in the Middle East."

Trump's visit to North Carolina on Monday coincided with concerns among his Republican allies that crippling damage from storm Helene will depress turnout in the battleground state's conservative mountain regions.

"Obviously, we want them to vote but we want them to live and survive and be happy and healthy, because this is really a tragedy," Trump said at a campaign stop in Swannanoa, population 5,300, after touring areas destroyed by the storm.

He said many Americans felt left behind by their federal government and renewed unsubstantiated claims that the response from the Biden administration has been slow, accusations the White House has rejected as misinformation.

The area hit hardest by Helene is deeply Republican. Trump won about 62% of the vote in 2020 in the 25 counties declared to be a disaster area after Helene, while Biden won about 51% in the remainder of the state, according to a Reuters analysis.

He said many Americans felt left behind by their federal government and renewed unsubstantiated claims that the response from the Biden administration has been slow, accusations the White House has rejected as misinformation.

Previously, Trump has falsely suggested officials were slow-walking aid to Republican pockets of the state. Democrats have said Trump's criticisms have made it harder for aid agencies to do their jobs.

Asked about an incident in which FEMA had to pause some operations after its employees received threats, Trump brushed the matter off.

"If FEMA were doing well, they'd be saying, 'Good job,'" Trump countered.