Several Republican rivals to Mr. Mastriano have been gathering on private conference calls in recent days in a last-minute attempt to stop him. All agree that he would be a drag on the party, though Mr. Mastriano has yet to sustain any serious coordinated attacks. Two rivals, State Senator Jake Corman and former Representative Lou Barletta, have set a joint event on Thursday, suggesting that the field might soon consolidate, at least slightly.

Democrats harbor their own fear: that the bleak 2022 political environment could nonetheless sweep into power Republicans who, in a less hostile climate, might seem unelectable.

“Like a lot of Democrats, I’m schizophrenic on this — rooting for the crazy person because it gives us the best chance to win. But at the same time it could give us a crazy senator or a crazy governor, or both,” said Mike Mikus, a Pennsylvania-based Democratic strategist…

In Pennsylvania, the governor appoints the secretary of state, the position that oversees state elections, meaning whoever wins the governorship will be overseeing the administration of one of the most coveted swing states in the 2024 presidential race.