Challengers see themselves in the Texas senator, even in races where their odds of an upset are considered steeper than Cruz’s surprise victory over a GOP establishment figure two years ago. He’s made endorsements in the Oklahoma and Nebraska Senate races, plus the Nebraska gubernatorial race, and sent almost $26,000 to federal candidates through his leadership PAC. “Ted Cruz would be extremely helpful as an endorser and a fundraiser,” said C. Edmund Wright, a consultant to longshot South Carolina Senate hopeful Lee Bright, in an email. “Rand Paul and Mike Lee would be great also.” But, he said, “the reason...