On a cool, sunny evening in April, John Fetterman, the junior senator from Pennsylvania, relaxed into the passenger seat of his robin’s-egg-blue Ford Bronco, which was parked just outside the U.S. Capitol. He was headed to his parents’ house, in York, Pennsylvania, where he grew up, and did not seem unhappy to be leaving Washington. A few hours earlier, in an elevator off the Senate chamber, he had closed his eyes and let his head slump against the control panel—whether from exhaustion or annoyance, it was hard to tell. Now, as an aide inched the Bronco through traffic, Fetterman mentioned that his Republican opponent in 2022, the TV doctor Mehmet Oz, had spent twenty-seven million dollars of his own fortune on the campaign. “And I’m, like, for what?” Fetterman said.…