In the midst of a critical stretch of the race for the Republican nomination, Ted Cruz dropped one of his top aides Monday for tweeting a story alleging that Marco Rubio had disparaged the Bible.

"This morning I asked for Rick Tyler's resignation," Cruz, a Texas senator, told reporters in Las Vegas ahead of the state's Republican caucus Tuesday. The actions of Tyler, who served as national spokesman, did not reflect the standards he wanted to uphold in the campaign, Cruz said. 

"We will conduct this campaign with the very highest standards of integrity. That has been how we've conducted it from day one," Cruz said. "Rick Tyler is a good man. This was a grave error of judgment." 

Tyler, who has helmed Cruz's messaging operation since he announced his presidential bid in March, sent a tweet Sunday linking to a news story that misquoted rival Rubio as having spoken negatively about the Bible. Tyler later deleted the tweet and apologized to the Florida senator.

"I should not have assumed the story was correct," Tyler wrote on Facebook. "I've deleted the post because I would not knowingly post a false story. But the fact remains that I did post it when I should have checked its accuracy first. I regret the mistake."

However, Cruz said Tyler's mistake was more than one of accuracy. "Even if it was true, we are not a campaign that's going to question the faith of another candidate," Cruz told reporters.

The Rubio campaign used the episode to continue hammering away at what it says is Cruz's questionable tactics. 

"Rick is a really good spokesman who had the unenviable task of working for a candidate willing to do or say anything to get elected," Rubio communications director Alex Conant said in a statement to Bloomberg Politics. "There is a culture in the Cruz campaign, from top to bottom, that no lie is too big and no trick too dirty. Rick did the right thing by apologizing to Marco. It's high time for Ted Cruz to do the right thing and stop the lies."

Republican front-runner Donald Trump took to Twitter to add more salt to the Cruz campaign's self-inflicted wound. 

"Ted Cruz has now apologized to Marco Rubio and Ben Carson for fraud and dirty tricks," Donald Trump tweeted. "No wonder he has lost Evangelical support!"

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Previously, Cruz dismissed the Rubio campaign's accusations of dirty tricks as fabrications lacking evidence. But he did apologize to Carson in February after his staff told Iowans that the retired neurosurgeon had dropped out of the race as they gathered to caucuses across the state.

Carson accepted the apology, but told CNN, "this is a cultural issue when people in your campaign feel that it's ok to distort the issues to their political advantage and to tell absolute lies."

—With assistance from Ben Brody and Terrence Dopp.

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