RIPON, Wis. — As she turns up the volume on her efforts to court disgruntled Republicans in her battle with former President Trump for the White House, Vice President Harris on Thursday teamed up with the most visible anti-Trump Republican in the town that claims to be the birthplace of the GOP.

Harris campaigned in battleground Wisconsin with former Republican Rep. Liz Cheney, a one-time rising conservative star in the GOP who, in the wake of the Jan. 6, 2021, riot on the U.S. Capitol, has vowed to do everything she can to prevent Trump from returning to power.

“I have never voted for a Democrat, but this year I am proudly casting my vote for Vice President Kamala Harris,” Cheney told the audience as she formally endorsed the Democrat presidential nominee. “As a conservative, as a patriot, as a mother, as someone who reveres our Constitution, I am honored to join her in this urgent cause.”

Harris praised Cheney as a leader who “puts country above party and above self, a true patriot.”

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The campaign event took place in Ripon, Wisconsin, where a one-room schoolhouse was designated a national historic landmark due to its role in holding a series of meetings in 1854 that led to the formation of the Republican Party.

Cheney, the daughter of former Republican Vice President Dick Cheney, once rose within the ranks of House Republican leadership.

But she was the most high-profile of the 10 House Republicans who voted to impeach then-President Trump in early 2021 on a charge of inciting the deadly January 6th riot at the Capitol, which was waged by right-wing extremists and other Trump supporters who aimed to disrupt congressional certification of President Biden’s Electoral College victory in the 2020 election.

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The conservative lawmaker and defense hawk immediately came under verbal attack from Trump and his allies and was eventually ousted from her No. 3 House GOP leadership position.

Cheney, who has been vocal in emphasizing the importance of defending the nation’s democratic process and of putting country before party, was one of only two Republicans who served on a special select committee organized by House Democrats that investigated the riot at the Capitol.

In 2022, she lost the GOP congressional primary in Wyoming to Harriet Hageman, a candidate backed by Trump.

At a speaking event in early September at Duke University in swing state North Carolina, Cheney announced that she would vote for Harris in the presidential election. Cheney’s father also endorsed Harris.

Cheney on Thursday warned that “our republic faces a threat unlike any we have faced before: a former president who attempted to stay in power by unraveling the foundations of our republic.”

She argued that Trump “can never be trusted with power again” and emphasized that “in this election, putting patriotism ahead of partisanship is not an aspiration, it is our duty.”

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

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Harris, speaking after Cheney, highlighted that “anyone who recklessly tramples on our democratic values as Donald Trump has, anyone who has actively and violently obstructed the will of the people and the peaceful transfer of power as Donald Trump has … must never again stand behind the seal of the president of the United States.”

And Harris also said that “I take seriously my pledge to be a president for all Americans.

Cheney was not always a fan of Harris.

The Trump campaign on Thursday repeatedly pointed to a social media post by Cheney during the 2000 election in which she said, “@KamalaHarris has a more liberal voting record than Bernie Sanders and Elizabeth Warren. Her radical leftist views-raising taxes, banning gun sales, taxpayer $ for abortion & illegal immigrant health care, eliminating private health insurance-would be devastating for America.”

Trump, speaking with Fox News’ Bill Melugin during a rally in Michigan on Thursday, said Cheney was “terrible” and “a stupid war hawk. All she wants to do is shoot missiles at people.”

On Cheney’s backing of Harris, Trump said, “I think they hurt each other. I think they’re so bad, both of them.”

The Cheneys are part of a growing list of prominent Republicans who are supporting Harris.

Two other high-profile anti-Trump Republicans, former Rep. Adam Kinzinger of Illinois and former Georgia Lt. Gov. Geoff Duncan, had speaking roles at the Democratic National Convention, which was held six weeks ago in Chicago.

And Harris is backed by more than 200 alumni who served in both Bush administrations or worked for the late Sen. John McCain and Sen. Mitt Romney, the 2008 and 2012 GOP presidential nominees, respectively. She’s also supported by more than 100 Republican former national security officials and other prominent Republicans.

Ripon is not the only town that claims to be the birthplace of the GOP. Exeter, New Hampshire, also has some bragging rites as it was the site of meetings in 1853 – a year ahead of the Ripon gatherings – by disenchanted political leaders who discussed the formation of a new party of Republicans.

But officials in Ripon said the group in Exeter never actually formed a political organization, or chose officials, as they did in Wisconsin.

Wisconsin is one of seven crucial battleground states with razor-thin margins that decided Biden’s 2020 White House victory and are likely to determine if Harris or Trump wins the 2024 presidential election.

With less than five weeks until Election Day in November, Harris and Trump are locked in a margin-of-error race in the key swing states.

While Trump retains vast sway over the GOP, even a small sliver of Republicans supporting Harris could make an important impact in what will likely be a race within the margins in the battleground states.

Get the latest updates from the 2024 campaign trail, exclusive interviews and more at our Fox News Digital election hub.