By STEVE PEOPLES and NANCY BENAC
Associated Press

LAS VEGAS (AP) – Ted Cruz is fighting to keep from spiraling out of contention.

Marco Rubio is fighting to prove he can build on his recent momentum.

And Donald Trump, with his rivals locked in a battle for second, is fighting for a third straight victory to expand a delegate lead that could soon become insurmountable.

Tuesday night’s Nevada caucuses force a critical test on the Republican Party’s leading presidential candidates.

"I think it’s the most unpredictable of all the races we’ve had so far. You go in really knowing less about this than any other election," said a less-than-confident Rubio. "We’ll see."

Cruz, a fiery conservative popular among voters on the GOP’s right, needs a spark to recover from one of the weakest moments of his campaign.

After denying charges of dishonest tactics for several weeks, the Texas senator on Monday asked for and received the resignation of a senior aide who spread an inaccurate news report suggesting Rubio had criticized the Bible. That was just days after Cruz finished a disappointing third in South Carolina after spending much of the past two weeks defending his integrity.

Another disappointing finish in Nevada’s low-turnout caucuses would raise new questions about Cruz’s viability heading into a crucial batch of Super Tuesday states on March 1.

"There’s something wrong with this guy," Trump said with his usual measure of tact during a massive Las Vegas rally Monday night. The former reality television star tweeted on Tuesday, "He used him as a scape goat-fired like a dog! Ted panicked."

Nevada’s caucusing takes place in schools, community centers and places of worship across the state – a process that’s been chaotic in the past.

"Please make sure you understand exactly where you’re supposed to be tonight, because there could be a lot of confusion," Rubio told supporters.

The state marks the first Republican election in the West, the fourth of the campaign. And it’s not one that’s gotten much attention from the GOP candidates.

Through Tuesday, the Republican candidates and the super PACs supporting them had spent a combined $3.8 million on television and radio advertisements in Nevada – less than a tenth of the $39.3 million spent ahead of last weekend’s South Carolina primary, according to Kantar Media’s CMAG data.

That primary reduced a GOP field that included a dozen candidates a month ago to five, with former Florida Gov. Jeb Bush the latest to drop out after a disappointing finish in South Carolina. Ohio Gov. John Kasich and retired neurosurgeon Ben Carson remain in the race and could play spoilers as the trio of leading candidates, Trump, Cruz and Rubio, battle for delegates with an increasing sense of urgency.

Trump’s rivals concede they are running out of time to stop him.

The election calendar suggests that if the New York billionaire’s rivals don’t slow him by mid-March, they may not ever. Trump swept all of South Carolina’s 50 delegates, giving him a total of 67 compared to Cruz and Rubio who have 11 and 10, respectively.

There are 30 delegates at stake in Nevada, awarded to candidates in proportion to their share of the statewide vote so long as they earn at least 3.33 percent. While proportional contests give Trump’s weaker rivals a chance to accumulate delegates, proportional contests also make it difficult to catch up if one candidate runs up a significant lead.

Rubio and Cruz have been laying into each other viciously in recent days, an indication they know Trump can be stopped only if one of them is eliminated. But neither of the first-term Hispanic senators is predicting victory in Nevada.

Rubio left the state before voting began, preferring to campaign in Minnesota and Michigan instead. He lived here as a boy, from grades 3 through 8 as his father tended bar and his mother cleaned hotel rooms. He told supporters Tuesday before heading out that he was the candidate who could best grow the GOP here – especially among its many Democratic-leaning casino workers.

"When I’m our nominee they will hear from us," Rubio said. "This is a city where tens of thousands of people are living how I grew up."

After finishing third in Iowa, fifth in New Hampshire and second in South Carolina, Rubio needs a win soon to support the idea that he is the prime heir to Bush’s supporters.

Indeed, Republican establishment heavyweights have been flooding to Rubio in recent days, including Arkansas Gov. Asa Hutchinson, North Carolina Sen. Thom Tillis and Utah Sen. Orrin Hatch. South Florida’s three Cuban-American members of Congress announced their support for him in the hours before the Nevada contest.

"We have incredible room to grow," Rubio says. After accusing Cruz of leading a campaign culture of "lies," the Florida senator asserted that Trump’s support is capped at roughly one-third of the Republican electorate.

"That means 65 percent of the party is against him," Rubio said. Once that 65 percent consolidates, he said, Trump will lose.

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Benac reported from Washington. Associated Press writers Nicholas Riccardi in Las Vegas and Chad Day in Washington contributed to this report.

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Follow Steve Peoples and Nancy Benac on Twitter at: http://twitter.com/sppeoples and http://twitter.com/nbenac

Copyright 2016 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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