Senator John Fetterman’s political loyalties have become an important question in Washington, with some of his fellow Democrats worrying that the Pennsylvanian could abandon the party just as it has an opportunity to claw back control of the Senate. In fact, Mr. Fetterman’s regular critiques of Democrats have made him so popular among Republicans in his home state that they now view him more warmly than Pennsylvania’s Republican senator, David Mc Cormick, according to a new poll from The New York Times, The Philadelphia Inquirer and Siena University. The Times/Inquirer/Siena poll, conducted last week, found that Mr. Fetterman had become far more popular with Republicans than with Democrats.

He was viewed favorably by 73 percent of self-identified Republicans, the poll found, compared with just 22 percent of Democrats. Only 63 percent of Republicans saw Mr. Mc Cormick favorably, though he appears significantly less known than Mr. Fetterman. Mr. Fetterman’s overall favorability rating of 46 percent is close to what it was the last time the Times/Inquirer/Siena poll tested it, in May 2024, when it was 48 percent. But back then, 74 percent of Democrats viewed Mr. Fetterman favorably and 64 percent of Republicans viewed him unfavorably.

That has now all but reversed, with 63 percent of Democrats viewing him negatively and most Republicans holding a positive view. Mr. Fetterman, who was first elected in 2022 and would face a challenging re-election bid if he runs again in 2028, has said that he will “never” switch parties. And despite his criticism of Democrats, he has remained a reliable vote for most of the party’s priorities in the Senate. But with both parties considering the possibility that Mr. Fetterman could emerge as a crucial swing vote in the Senate after the midterms, his loyalty to Democrats is being watched closely.

Last month, he and Mr. Mc Cormick established a joint fund-raising committee, a rare development for prominent lawmakers from opposing parties. Mr. Fetterman’s fierce support of Israel during the war in Gaza is a primary source of tension with his fellow Democrats.