Most are staying mum, plan to be neutral to avoid angering Donald Trump supporters back home or say Cruz needs to do more outreach to win over GOP senators whom he has dubbed as part of the "Washington cartel."
It's a reminder that many Republican establishment senators are still uncomfortable with the Texas senator despite their fear of Trump, the party's presidential front-runner.
Sen. Marco Rubio refused to say in an interview with CNN if he'd back Cruz.
"I'm not talking about the campaign today other than I'm pleased with the result in Wisconsin that Donald Trump didn't win."
Rubio had told supporters when he was a candidate that he'd barnstorm across the country in his pickup truck to stop Trump. Asked about that, Rubio said: "I'm not having anything to announce on that today other than to tell you that I obviously think if Donald Trump is the nominee of our party, it will fracture it. And that's all I'm prepared to say."
CNN reported earlier this week that Rubio is getting pressure from donors to stay neutral, partly because Rubio and Cruz could presumably face off again in a 2020 rematch and most don't think Rubio's endorsement would amount to much. But Rubio is holding onto his pledged delegates
, which benefits Cruz, and he's asked states to remove his name from primary ballots to avoid siphoning off the anti-Trump vote.
Just two senators have backed Cruz, including his friend, Mike Lee of Utah, and Sen. Lindsey Graham of South Carolina, who is an outspoken Trump detractor.
But one more senator might add his support: Montana Sen. Steve Daines, a freshman whose state votes June 7 and could have an outsized role in the nominating contest. Daines told CNN he's traded voicemails with Cruz and is considering an endorsement.
"We're still kicking the tires," Daines said.
Daines spokeswoman Marcie Kinzel later said, "He is kicking the tires -- not going on a test drive."
And on Thursday night another GOP senator reluctantly was backed into supporting Cruz.
Sen. Jim Risch of Idaho told Wolf Blitzer
on CNN's "The Situation Room," that he "hopes" his Texas colleague will win the GOP nomination because he's the only viable choice among the candidates for the Republican nomination.
Reminded that only Sens. Lee and Graham are backing Cruz so far, Risch asked, "Did I just endorse, Wolf?"
"You sort of said you prefer him over the two," Blitzer responded, to Risch's agreement. "That sounds like an endorsement, doesn't it?"
"I guess," Risch replied. "It depends on your definition."
In states with upcoming primaries, GOP senators are mum on whether they'll endorse Cruz. This includes Sen. Dan Coats of Indiana, who has openly criticized Cruz's tactics, Sen. Mike Rounds of South Dakota and Sen. Pat Toomey, who faces a tough re-election fight in Pennsylvania.
"I have no plans to at this time," Toomey said.
Nebraska Sen. Ben Sasse, a sharp critic of Trump's, declined to comment on if he'd endorse Cruz before his state's May 10 primary.
Republican senators have called for Cruz to repair poor relations after two years of infighting, but Cruz has yet to schedule any air-clearing
meeting with his colleagues. One senator with clout on the right, Iowa Sen. Joni Ernst, said she did not plan to endorse during the primary.
"No endorsement," she said.
And a former Rubio supporter, Arizona Sen. Jeff Flake, said he planned to be neutral.
"I've killed enough candidates already," he said.