The Democratic senator John Fetterman, who has faced mounting political challenges, is joining forces with the Republican senator Dave McCormick to launch a new joint fundraising committee, a move that is likely to fuel additional questions about Fetterman’s increasingly rightward lurch.

Pennsylvania’s two US senators have established a shared fundraising committee that will collect donations benefiting both of their campaigns in an unusual bipartisan arrangement.

Federal Election Commission records filed on Monday show the creation of Common Ground PA. The filing identifies the leadership Pacs and principal campaign committees for both Fetterman and McCormick as participants in the joint committee. Politico first reported the formation of the fundraising committee this week.

The move led to fresh speculation that Fetterman might be planning a party switch. Rick Wilson, the longtime political consultant and anti-Trump activist, predicted “He’s gonna flip” in a social media post in response to the new fundraising committee.

Nick Field, a local politics writer in Pennsylvania, wrote: “Fetterman caucusing with the Republicans in 2027, and even trying to run in 2028 with their support, looks likelier and likelier by the day.”

Mike Nellis, a Democratic political strategist, said that Democrats should assume that Fetterman “is a Republican going forward, and we can’t rely on his vote – especially when it comes to judges”.

Fetterman built his reputation in 2016 as a vocal progressive and an early backer of Bernie Sanders’ presidential campaign. In the years since, however, he has steadily moved away from many of his earlier left-leaning positions, emerging as a bipartisan lawmaker who has increasingly found common ground with Republicans.

Since Donald Trump began his second term, Fetterman has repeatedly broken with fellow Democrats on key issues. He was the only Democrat to support the confirmation of several of Trump’s cabinet nominees, has backed parts of the administration’s immigration enforcement agenda and has supported the US war with Iran. As a result, Fetterman has faced repeated criticism from members of his own party.

Fetterman’s next re-election campaign will take place in 2028, while McCormick does not face voters again until 2030. According to the latest Federal Election Commission filings, Fetterman for PA reported approximately $1.99m in cash on hand.

Although they represent opposing political parties, Fetterman and McCormick have collaborated on multiple issues and have publicly referred to each other as close friends. Last month, they appeared together in Philadelphia to encourage Pennsylvania parents to sign their children up for Trump accounts.

Neither senator currently holds a majority approval among Pennsylvania voters. A Quinnipiac poll from February found that 46% approved of Fetterman’s overall job performance, while McCormick received a 37% job approval rating.

Writing in a Washington Post opinion piece in May, Fetterman said: “Being an independent voice that works with the other side to deliver for Pennsylvanians might put me at odds with the party that I have stayed committed to and have no plans to leave – but I will continue to put the commonwealth and the country first. Plus, I’d be a terrible Republican who still votes overwhelmingly with Democrats.”