PENNSYLVANIA, United States (AFP) —Kamala Harris tore into “unhinged” Donald Trump Monday over his threat to set the US military on political opponents, as the presidential rivals held duelling events in battleground Pennsylvania.

Early voting is underway in most of America, with polling suggesting an agonisingly tight race nationally and a margin-of-error tussle in Pennsylvania and the other hotly contested swing states likely to determine the outcome.

With the high-octane election tightening in the home stretch, Harris has been making a campaign issue of the Republican ex-president’s increasingly authoritarian rhetoric that has prompted accusations that he is co-opting the language of fascism.

At a rally in Erie, the most evenly divided of Pennsylvania’s counties, the Democratic vice-president played a video montage of Trump calling for the jailing of political opponents and repeatedly referring to “the enemy from within”.

It included a weekend interview on Fox News in which Trump suggested “sick people, radical-left lunatics” could be “very easily handled” by the military under a Trump Administration.

Harris said Trump would persecute groups he has targeted before, including journalists, election officials, and judges who “insist on following the law, instead of bending to his will”.

“This is among the reasons I believe so strongly that a second Trump term would be a huge risk for America, and dangerous,” she warned.

“Donald Trump is increasingly unstable and unhinged — and he is out for unchecked power.”

While Trump has been hitting Harris over Biden Administration policies, her race, and her intelligence, Harris has sought to cast the Republican as a risky choice who cares more about creating fear than solving problems.

Trump has been calling his domestic political rivals “scum” and touting his relationships with foreign dictators while his running mate, JD Vance, has repeatedly refused to acknowledge that Trump lost the 2020 election.

Trump — at 78 the oldest major-party presidential candidate ever — has also rejected calls to make public his medical records as candidates normally do, and has refused to release his tax records for the third-straight election.

With three weeks to go Trump and Harris remain locked in a bitter, neck-and-neck battle for the swing states, of which blue-collar Pennsylvania is the biggest prize.

And alarm bells have been ringing over Harris’s momentum, with her support stagnant at around 49 per cent in polling since mid-September.

Aides are concerned, in particular, about an erosion of support among black voters — a key pillar in the Democratic coalition that is 15 points behind where it was for Biden when he narrowly defeated Trump in 2020.

A New York Times/Siena poll last week found Harris with 78 per cent support among black voters against around 90 per cent support for Democrats in recent presidential elections, with men accounting for most of the drop-off.

Harris and running mate Tim Walz — who called Trump “fascist to his core” at his own campaign event in Wisconsin — will this week blanket Michigan, Wisconsin and Pennsylvania.

The traditionally Democratic Rust Belt states represent her likeliest path to the presidency, and she is expected to campaign with a particular focus on black male voters.

In Erie, Harris touted her “opportunity agenda”, which includes small business loans and training programmes for African American men, as well as a health initiative focused on diseases that disproportionately impact the community.

She will sit down this week with popular black media figures, including a town hall-style event in Detroit on Tuesday with The Breakfast Club co-host Charlamagne Tha God.

Trump, who is doing better with black voters than any Republican candidate since Richard Nixon in 1960, pledged at a town hall on the outskirts of Philadelphia to slash household energy bills.

Asked about how he would tackle inflation Trump said, “We’re going to do a lot of things,” before pivoting to border security and media criticism of him repeatedly bringing up fictional serial killer Hannibal Lecter at his campaign events.

Turning to his prospects in November’s election he told his cheering audience: “Our poll numbers have gone through the roof with blacks and Hispanics, have gone through the roof. And I like that.”