Democratic presidential nominee and U.S. Vice President Kamala Harris and Congresswoman Liz Cheney (R-WY) interact during a campaign event at Ripon College in Ripon, Wisconsin, U.S., October 3, 2024. REUTERS/Evelyn Hockstein / Reuters

Former Republican Congresswoman Liz Cheney and Democratic presidential candidate Kamala Harris said former President Donald Trump is not fit to lead the U.S., urging voters to put country over party as they campaigned together on Oct. 3.

Cheney and her father Dick Cheney, who was vice president under George W. Bush and is still vilified by Democrats for his bullish defense of the Iraq War, are staunch conservatives and two of the most prominent Republicans to have endorsed Harris against Trump in the Nov. 5 election.

Both have sharply criticized Trump, the Republican nominee, calling his refusal to accept his 2020 election loss and his role in the Jan. 6, 2021 attack on the U.S. Capitol disqualifying.

"I was a Republican even before Donald Trump started spray tanning," Cheney joked at the event in Wisconsin, describing herself as a Ronald Reagan conservative. "I am proudly casting my vote for Vice President Kamala Harris," she said, her first vote ever for a Democrat.

Cheney's comments could help Harris as she tries to court Republican and centrist voters in what polls show to be a very tight race with Trump.

To win, Harris needs to win over Republicans and independents wary of him without alienating her base, particularly in states like Wisconsin that can swing toward Republican or Democrat and are likely to decide the election.

Cheney was the top Republican on the House of Representatives committee that investigated the Jan. 6 riot, earning Trump's disdain and effectively exiling her from the party.

"Our republic faces a threat unlike any we have faced before," Cheney said, pointing to Trump's efforts to overturn the 2020 election results.

"What January 6th shows us," Cheney said, "is that there is not an ounce, not an ounce, of compassion in Donald Trump. He is petty, he is vindictive and he is cruel. And Donald Trump is not fit to lead this good and great nation."

On Oct. 2, a judge unsealed a 165-page court filing outlining federal prosecutors' case against Trump for his attempt to overturn his 2020 election defeat. Trump has pleaded not guilty to charges of conspiracy and obstruction.

Cheney said she and Harris may disagree on some things but they are bound together by their duty to the Constitution. Harris will be a president "who will defend the rule of law," Cheney said.

"She's working to unite reasonable people from all across the political spectrum," she said. "I'm honored to join her in this urgent cause."

Harris has adopted a center-to-right-leaning stance on several issues, including her staunch support for Israel, a border policy tough on migrants and an all-of-the-above energy strategy to keep fuel costs low.

Kathy Rubino, 74, a retired nurse practitioner and an independent at the Wisconsin event, said she plans to vote for Harris and praised Cheney.

"She's representing who she thinks is best for the country," Rubino said. "She stood up for what she believed, and that's the important thing here."

Recent polling shows Harris struggling to gain traction with Republican voters despite getting the public support of hundreds of former and current Republican officials in the military, national security and local governments.

While Harris led Trump 47 percent to 40 percent among all voters in a Sept. 20-23 Reuters/Ipsos poll, only 5 percent of the poll's Republican respondents said they would back her, a figure close to the margin of error. Ten percent said they would vote for another candidate, did not know who they would vote for or would not vote.

At Oct. 3, event, Harris praised Cheney - who opposed same-sex marriage and praised the Supreme Court's repeal of the right to abortion - for putting her country above her party and called the endorsement a "profound honor."

"There are many who know it's wrong and then there are those who have the courage to speak out loudly about it," Harris said of Cheney's criticism of Trump.

Harris repeated her message from the Democratic Convention that she would be a president for all Americans regardless of party, and also described Trump as unfit to hold the office.

The event was held in Ripon, Wisconsin at a one-room schoolhouse significant to the Republican party: it was the site of meetings that led to the party's formation in 1854 and is referred to as the party's birthplace.