WASHINGTON (Reuters) - Republican presidential candidate Marco Rubio received boosts Monday in his drive to become the mainstream Republican alternative to front-runner Donald Trump, with a string of high-profile endorsements and missteps by rival Ted Cruz’s campaign.

U.S. Republican presidential candidate Marco Rubio speaks with reporters before departing from the airport in Las Vegas, Nevada February 22, 2016. REUTERS/Chris Keane

Rubio, who eked out a second-place finish in South Carolina’s primary by fewer than 1,000 votes over Cruz on Saturday, racked up endorsements from prominent Republicans including U.S. Senator Orrin Hatch of Utah, Arkansas Governor Asa Hutchinson and former presidential candidate Bob Dole.

Rubio and Cruz came out of South Carolina with sharper criticism of Trump, who swept the Southern state with a comfortable margin of victory. At the same time, the two senators’ rivalry intensified - and soured.

Cruz fired his main spokesman, Rick Tyler, on Monday afternoon over a video that falsely showed Rubio dismissing the Bible.

Tyler had apologized late on Sunday for posting “an inaccurate story” involving a video purporting to show Rubio referring to the Bible and saying, “Not many answers in it.” Tyler had retweeted a link to the misleading video and posted it on Facebook.

Cruz fired Tyler the next day, saying his campaign did not question the faith of other candidates. “That’s why I’m asking for Rick Tyler’s resignation,” Cruz said.

The first-term senators from Texas and Florida are locked in a battle to become their party’s alternative to political outsider Trump in Nevada’s caucus on Tuesday, the last Republican presidential contest before the busy voting month of March.

Tyler’s dismissal came amid intense criticism of the Cruz campaign as dishonest from both Rubio and Trump.

Rubio spokesman Alex Conant called Cruz a “candidate willing to do or say anything to get elected” and urged him to apologize.

“There is a culture in the Cruz campaign, from top to bottom, that no lie is too big and no trick too dirty,” he said.

Trump seized the opportunity to pile on Cruz, whom he has repeatedly characterized as a liar.

“Wow, Ted Cruz falsely suggested Marco Rubio mocked the Bible and was just forced to fire his Communications Director. More dirty tricks!” the billionaire businessman from New York said on Twitter.

“Ted Cruz has now apologized to Marco Rubio and Ben Carson for fraud and dirty tricks. No wonder he has lost Evangelical support!,” continued Trump, who has derided Cruz for failing to live up to expectations he would get solid support from evangelical Christians in South Carolina.

Trump was the big winner in that state on Saturday, finishing ahead of Rubio by 10 percentage points.

Opinion polls show Rubio and Cruz running close in Nevada, and both candidates hope to get a boost going into the contests in a dozen states on March 1. Super Tuesday is the crown jewel in the state-by-state nominating contests to pick the Republican and Democratic candidates for the Nov. 8 presidential election.

Rubio on Monday also secured the backing of three Republican leaders from Nevada: U.S. Senator Dean Heller and U.S. Representatives Cresent Hardy and Mark Amodei.

Senator Hatch said that, unlike many in the Republican establishment, he did not dislike Trump.

“I just feel that Rubio is the more serious candidate. And I feel he has the background to be able to really help turn this mess around,” Hatch told Reuters.