By STEVE PEOPLES and MARY CLARE JALONICK, Associated Press

MIAMI (AP) — As high-stakes elections loom in Florida and Ohio, anxious Republican officials are coming to terms with the idea that their second-least-favorite GOP presidential candidate —Texas conservative Ted Cruz — may be the party's last best chance to stop Donald Trump.

Trump, in turn, is renewing his vigorous criticism of the Texas senator, casting the rival he calls "Lying Ted" as too polarizing to break the Washington gridlock or win a general election.

Photos: The Many Faces of Donald Trump View All 17 Images

"The problem with Ted is that he'll never get anything done," Trump told CNBC's "Squawk Box" on Thursday. "And the bigger problem is that it's impossible for him to get elected."

Some of Cruz's would-be backers have those same fears. But they fear the prospect of a Trump candidacy more.

The two men were to clash again on the debate stage Thursday night in Miami, along with Marco Rubio and John Kasich who are fighting with Cruz to emerge as the strongest alternative to Trump. For now at least, Cruz appears to be ahead in that contest.

Possible Cruz supporters include reluctant Senate colleagues and former presidential rivals with strong ties to major donors. The first-term senator announced the backing of one former primary opponent, Carly Fiorina, on Wednesday and is seeking the backing of another, Jeb Bush, on Thursday.

"Donald Trump needs to be beaten at the ballot box," Fiorina declared Thursday on MSNBC's "Morning Joe."

On Capitol Hill, former Cruz adversary, South Carolina Sen. Lindsey Graham, has reluctantly embraced the idea of a Cruz nomination.

"It's an outsider year, and the most logical person to take on Trump based on past performance is Ted Cruz," Graham said. Earlier in the year, Graham likened the choice between Cruz and Trump to "being shot or poisoned."

"He's not my preference," Graham said of Cruz. "But we are where we are. And if Trump wins Florida and Ohio, I don't know if we can stop him."

Indeed, next Tuesday's winner-take-all contests in Florida and Ohio have injected a sense of urgency into the GOP's anti-Trump movement.

The celebrity businessman's critics hope to capitalize on what they see as another inflammatory reference about Muslims. "I think Islam hates us," he said late Wednesday on CNN. "There's a tremendous hatred. We have to get to the bottom of it."

At the same time, Trump is calling on mainstream Republicans to unify behind hm.

"Whatever the establishment is, they should embrace what I've done," he said on CNBC.

He continued: "If for some reason I don't make it or it ends, I don't get there, they're going to have millions and millions of people that are going to walk away from the polls and never vote and the Democrats are assured of victory."

Bush planned to confer with the other candidates — save Trump — ahead of Thursday's debate. He met privately with Florida Sen. Rubio on Wednesday, and planned to meet with Cruz and Ohio Gov. Kasich on Thursday.

Bush and Trump engaged in heated confrontations throughout Bush's campaign, repeatedly referring to each other as "loser."

The GOP establishment's favorite, Florida Sen. Marco Rubio, picked up where Bush left off, but struggled badly in this week's round of primary contests, failing to pick up a single delegate. Trump won three contests and Cruz won one.

Now, in the midst of a weeklong march through Florida to save his candidacy, Rubio concedes that he went too far in insulting Trump.

"My kids were embarrassed by it, and if I had it to do over again I wouldn't," Rubio said on MSNBC Wednesday night.

Rubio's weak standing has forced some of his supporters to consider Cruz.

"I could see myself as a Cruz supporter," Nevada Sen. Dean Heller, a Rubio backer, said Wednesday. "I agree with Cruz 80 percent of the time. There are things I don't agree with him on, but if we are agreeing 80 percent of the time and he's a conservative, we are going to get along just fine."

Still, no Republican senator has endorsed Cruz, who called Majority Leader Mitch McConnell a liar and helped engineer the 16-day partial government shutdown in 2013. Half a dozen Senate Republicans said Wednesday that they hadn't heard from either Trump or Cruz.

Trump has one Senate endorsement, from Alabama's Jeff Sessions, while Rubio has endorsements from 14 senators.

On the Democratic side, Clinton and Bernie Sanders tangled Wednesday night over who's a true advocate for Latinos.

The former secretary of state faulted Sanders for repeatedly voting against a 2007 comprehensive immigration reform bill; he faulted her for opposing a 2007 effort to allow people who were in the country illegally to obtain driver's licenses.

Sanders surprised Clinton with a win Tuesday night in Michigan, a victory that breathed new life into his White House bid. But Clinton, who won Mississippi, padded her delegate lead and is now halfway to the number needed to clinch the nomination.

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Jalonick reported from Washington. AP writers Julie Pace in Miami, and Donna Cassata, Alan Fram and Andrew Taylor in Washington contributed to this report.