Liz Cheney, a former Republican congresswoman and longtime opponent of abortion rights, on Monday condemned Republican-imposed bans on the procedure and urged conservatives to support Kamala Harris for US president.

Cheney was speaking at the first of three joint events with the vice-president in the suburbs of three swing states aimed at prising moderate Republican voters away from party nominee Donald Trump. She has become the Democrat’s most prominent conservative surrogate and is rumoured to be in contention for a seat in a potential Harris cabinet.

At the first event in Malvern, a Philadelphia suburb, against a blue backdrop that said “a new way forward” and red one that said “country over party”, Cheney suggested that Republican-led states have overreached in restricting abortion since the supreme court’s 2022 Dobbs decision ended it as a constitutional right.

“I think there are many of us around the country who have been pro-life, but who have watched what’s going on in our states since the Dobbs decision and have watched state legislatures put in place laws that are resulting in women not getting the care they need,” said Cheney, 58, a former Wyoming congresswoman and daughter of former vice-president Dick Cheney.

“I think this is not an issue that we’re seeing break down across party lines, but I think we’re seeing people come together to say: what has happened to women, when women are facing situations where they can’t get the care they need, where in places like Texas, for example, the attorney general is talking about suing, is suing, to get access to women’s medical records … that’s not sustainable for us as a country and it has to change.”

Harris, who turned 60 on Sunday, nodded repeatedly and applauded in response. The audience also clapped warmly.

It was a striking attempt to build a permission structure for conservatives to back Harris, who has made reproductive freedom a centrepiece of her campaign and vowed to restore the protections of Roe v Wade if authorised by Congress. Cheney, by contrast, has an A rating from Susan B Anthony Pro-Life America, a group that grades members of Congress based on their anti-abortion credentials.

Monday’s three events in Pennsylvania, Michigan and Wisconsin were being held in counties won by Nikki Haley in the Republican presidential primary. Haley, a former South Carolina governor and US ambassador to the United Nations, had sought to neutralise abortion as an election issue by supporting states’ autonomy and rejecting calls for a national ban.

Cheney has vocally opposed Trump since the January 6 insurrection at the US Capitol. Her recent endorsement of Harris fuelled speculation that she could play a part in a future Harris administration.

Earlier this month, appearing on the popular daytime talkshow The View, Harris said she would differ from Joe Biden by including a Republican in her cabinet. She was asked by radio host Howard Stern if that might be Cheney but avoided a direct answer. Appointing Cheney would carry considerable political risks given her hawkish foreign policy and her father’s role in instigating the Iraq war.

Trump has frequently tried to paint Harris, who is from deep blue California, as a radical liberal but she struck a moderate tone during her appearance with Cheney, who lost her House seat after she co-chaired a congressional committee that investigated the January 6 attack.

Harris promised to “invite good ideas from wherever they come” and “cut red tape,” and she said “there should be a healthy two party system” in the country. “We need to be able to have these good intense debates about issues that are grounded in fact,” she said.

“Imagine!” Cheney responded.

“Let’s start there!” Harris said as the audience clapped. “Can you believe that’s an applause line?”

Voters in Chester county, which includes Malvern, narrowly voted for Republican Mitt Romney in 2012 but the county was won by Hillary Clinton by nine percentage points in 2016 and Biden by 17 points in 2020.

The discussion was chaired by Sarah Longwell, who runs the group Republican Voters Against Trump, and lasted 40 minutes including two questions from the audience.

Cheney praised Harris, saying: “I’m a conservative. I know that the most conservative of all conservative principles is being faithful to the constitution. You have to choose in this race between someone who has been faithful to the constitution, who will be faithful, and Donald Trump.”

The former congresswoman said she was concerned about allowing a “totally erratic, completely unstable” Trump to run foreign policy. “Our adversaries know that they can play Donald Trump,” she said. “And we cannot afford to take that risk.”

But some observers questioned the wisdom of campaigning with Cheney in Michigan, which has the highest concentration of Arab Americans in the country, given her hawkish foreign policy and her father’s role in instigating the Iraq war. Many such voters are now wavering or abstaining because of the Biden-Harris administration’s handling of the crisis in Gaza.

Trump weighed in on Monday, writing on his Truth Social platform: “Arab Voters are very upset that Comrade Kamala Harris, the Worst Vice President in the History of the United States and a Low IQ individual, is campaigning with ‘dumb as a rock’ War Hawk, Liz Cheney, who, like her father, the man that pushed Bush to ridiculously go to War in the Middle East, also wants to go to War with every Muslim Country known to mankind.”

The Michigan event was held in Royal Oak, outside Detroit, and moderated by Maria Shriver, a journalist and former first lady of California.

In a nod to the concept of shy Harris voters who would rather not share their views publicly, Cheney said: “If you’re at all concerned, you can vote your conscience and not ever have to say a word to anybody and there will be millions of Republicans who do that on November 5.”

Harris said voters should take Trump’s rhetoric seriously rather than writing it off as some “sick sense of humour”. She noted that retired general Mark Milley, who served as chairperson of the joint chiefs of staff under Trump, reportedly described him as “fascist to the core”.

Harris said: “Some people find it humorous, what he says, and think it’s just silly, but understand how brutally serious it is … Anyone who has openly said, as he has, that he would terminate the constitution of the United States should never again stand behind the seal of the president of the United States.”

Cheney added: “In the election we need to elect the person who is the responsible adult.”

In a lighter moment, Shriver asked Harris about what she is doing to de-stress, noting that Americans say they are turning off the news, doing yoga, “eating gummies, all sorts of things”.

Harris replied, “Not eating gummies!” and burst into laughter. She admitted: “I wake up in the middle of the night usually these days, just to be honest with you, but I work out every morning. I think that’s really important to just kind of – you know, mind, body and spirit … My family grounds me in every way.”

But Harris counselled against despair: “Let’s not feel powerless ... because then we have been defeated and that’s not our character as the American people.”

More than a hundred former Republican officeholders and officials joined Harris last week in Washington Crossing, Pennsylvania, not far from where general George Washington led hundreds of troops across the Delaware River to a major victory in the revolutionary war. At a rally there, Cheney told Republican voters that the patriotic choice was to vote for Democrats.