Then he found a lifeline: As Mr. Sheehy has told the story over the years, Stephen Schwarzman, the billionaire chairman of the private equity group Blackstone Inc., helped steer a $150 million investment from his company into Mr. Sheehy’s.

Both Mr. Schwarzman and Mr. Sheehy came out winners. Blackstone nearly doubled its investment by cashing in many of its shares a few years later, even as the firefighting company continued to struggle. Mr. Sheehy collected multi-million-dollar bonuses that helped him seed his Republican Senate campaign in 2024.

It was an uphill race against a popular, three-term Democratic incumbent, Jon Tester. But with control of the Senate up for grabs and Mr. Sheehy one of the few who could help tip it in favor of Republicans, Mr. Schwarzman came to his aid once again, hosting a fund-raiser for him and also donating $8 million to a political action committee that supported his candidacy.

He was not the only financial heavyweight in Mr. Sheehy’s corner.

At least 64 billionaires and 37 of their immediate family members donated directly to his campaign, a New York Times analysis found. When also accounting for money that flowed through political committees that support Mr. Sheehy, an analysis shows that billionaires contributed about $47 million in the race that Mr. Sheehy went on to win.