In interviews with POLITICO, some of Rubio’s endorsers and quiet supporters are openly weighing backing Ted Cruz — who is almost universally loathed within the Republican conference but viewed increasingly as a better option than Donald Trump.

Indeed, once Rubio is swept aside, Cruz may be the only option if GOP senators want to stop Trump.

“I could see myself as a Cruz supporter,” said Sen. Dean Heller (R-Nev.), who endorsed Rubio after Jeb Bush faltered. “There’s some things I don’t agree with him on but if I agree with him 80 percent of the time and he’s a conservative, we’re going to get along just fine.”

And while his most optimistic supporters spun away Rubio’s dreadful Tuesday performance as a tactical choice not to focus on states like Mississippi and Michigan, his backers on Capitol Hill agree: If he doesn’t win Florida, his viability officially plummets to zero.

“I think everyone knows that,” said Sen. Jeff Flake (R-Ariz.), another Rubio backer.