US Vice President Kamala Harris has rallied with Republican Liz Cheney in US conservative heartland, the pair delivering a twin denunciation of Donald Trump as a dire threat to democracy.

With some people hoisting signs reading “country over party”, Harris told the crowd in Wisconsin on Thursday (local time) that “people of every party must stand together” to reject Trump, citing his refusal to accept the results of the 2020 election and his failure to quell the insurrection of January 6, 2021.

It was an improbable moment, a Democratic nominee giving a nod to a rival party member and to the origins of the opposing party in the closing weeks of a presidential campaign. It also demonstrated how much Harris is trying to win over moderate and crossover Republican voters.

“He refused to accept the will of the people and to accept the results of an election that was free and fair,” Harris said of Trump.

“The president of the United States must not look at our country through the narrow lens of ideology or party partisanship or self-interest.

“Our nation is not some spoil to be won. The United States of America is the greatest idea humanity ever devised.”

Thursday’s rally was held in Ripon, home to the white schoolhouse where meetings in 1854 to oppose slavery’s expansion led to the start of the Republican Party.

It also came as CNN reported that Cheney was poised to join three other previously pro-Trump Republican women to make the case against Trump’s re-election.

The network said former Trump White House aides Alyssa Farah Griffin, Cassidy Hutchinson and Sarah Matthews would sit down with Cheney in a fireside chat in Pennsylvania next week to “offer a warning about the threat Donald Trump poses to democracy and the rule of law”. They will reportedly make the case about “the need for independents, moderates, and Republicans to stop him from getting back in office”.

The event is not an official Harris campaign outing, but is expected to be the first of many for the group in the so-called battleground states.

Cheney is one of Trump’s most ardent antagonists. The daughter of former Republican vice-president Dick Cheney, she was the top Republican lawmaker on the House committee that investigated the January 6, 2021, insurrection, earning Trump’s disdain and effectively exiling herself from her own party.

“Violence does not and must never determine who rules us. Voters do,” Cheney told the Wisconsin crowd as she recounted Trump refusing to act as he watched the violent attack on television.

Someone in the crowd yelled “coward!”. Others booed.

“Donald Trump was willing to sacrifice our Capitol, to allow law enforcement officers to be beaten and brutalized in his name, and to violate the law and the Constitution in order to seize power for himself,” Cheney said.

“I don’t care if you are a Democrat or Republican or an independent, that is depravity and we must never become numb to it.”

Adding to the surreal nature of the event, the crowd cheered references to Dick Cheney and to another Republican former vice-president: Mike Pence, who refused to bow to pressure from Trump and attempt to stop the certification in Congress of Biden’s 2020 victory.

In an interview Thursday night with Fox News Channel, Trump said of Harris and Cheney: “I think they hurt each other. I think they’re so bad, both of them.”

Cheney lost her Wyoming seat to a Trump-endorsed candidate two years ago and endorsed Harris, the Democratic nominee, in September.

“I know that she loves our country, and I know she will be a president for all Americans,” Cheney said of Harris.

Noting that she remained conservative, Cheney said she was “honoured to join her in this urgent cause”.

Harris is on a two-day Wisconsin and Michigan swing, while Trump was in Michigan on Thursday as both candidates grapple for wins in the “blue wall” battleground states, which also include Pennsylvania.

SHAMEFUL! The Radical Democrats, led by Comrade Kamala Harris and Deranged Jack Smith, are lying to the American People, and trying to hide the fact that I specifically said, “PEACEFULLY AND PATRIOTICALLY” to the huge crowd of Patriots gathered in Washington, D.C. on January 6th.…

— Donald J. Trump Posts From His Truth Social (@TrumpDailyPosts) October 3, 2024

While Cheney and Harris spoke, the former president took his social media site to say Democrats and prosecutors had lied about the “huge crowd of Patriots gathered in Washington, DC on January 6th”.

That was a far cry from President Joe Biden’s reaction. Arriving back at the White House after touring damage from Hurricane Helene in Georgia and Florida, Biden said of Cheney: “She made one of the most consequential speeches I’ve ever heard. She has character.”

“I know her dad. We argue like hell, but I always admired his courage and honesty. What she did not took only political courage, but physical courage,” Biden said.

Harris’ visit to Wisconsin came a day after a federal judge unsealed a 165-page court filing outlining prosecutors’ case against Trump for his attempt to overturn his 2020 election defeat.

Trump has pleaded not guilty to charges of conspiracy and obstruction.