Just review the results: In races where he’s endorsed 2014 candidates facing competitive primary challenges, he’s undefeated so far. He was the star of a U.S. Chamber of Commerce ad endorsing Rep. Mike Simpson of Idaho that aired in mid-April, around the same time the congressman pulled away from his tea-party-backed challenger Bryan Smith. He backed pediatric neurosurgeon Monica Wehby in the Oregon Senate race, giving the political outsider a degree of establishment credibility. And he was one of the first Republican officials to jump on the Joni Ernst bandwagon in Iowa, endorsing the upstart Senate candidate when she was still lagging in the polls. (He’s headlining two events for Ernst on Friday in Cedar Rapids and Davenport, his first campaign rallies of the cycle.)

While many politicians endorse candidates who are safe bets to win primaries, the normally risk-averse Romney has eagerly put his reputation on the line, backing candidates in next month’s primaries who face challenging odds. In California, Neel Kashkari is vying to finish ahead of tea-party candidate Tim Donnelly in the governor’s race, while Romney-endorsed Nevada state Sen. Mark Hutchison is hoping to defeat former Senate candidate Sue Lowden in the state’s lieutenant governor’s primary. In Colorado, he weighed in on behalf of former Rep. Bob Beauprez, running in a competitive gubernatorial primary. And Romney just announced support for former Paul Ryan aide Elise Stefanik, facing well-funded opposition running for a New York congressional seat from GOP businessman Matt Doheny.

“He’s not afraid to make a choice. He sees a candidate who he thinks will be good and have a shot at winning, he’s going to get involved,” said Tom Rath, a longtime Romney adviser who remains in touch with the former presidential nominee.