TALLAHASSEE, Fla. – A national group that helps Republicans get elected to the Senate is pressuring GOP Gov. Charlie Crist to drop out of the Florida Senate race rather than run as an independent. 

Rob Jesmer, executive director of the National Republican Senatorial Committee, said in an e-mail to political consultants Monday that the committee believes there is “zero chance” Crist will continue running as a Republican against former state House speaker Marco Rubio. 

A recent poll showed Crist is trailing Rubio badly in the GOP primary but could win a three-way race with him and likely Democratic nominee U.S. Rep. Kendrick Meek. Speculation is that Crist will quit the primary and run as an independent. 

“If Governor Crist believes he cannot win a primary then the proper course of action is he drop out of the race and wait for another day,” Jesmer said. 

It’s the latest sign of how far Crist’s campaign has fallen in less than a year. Last May, Committee Chairman Sen. John Cornyn, R-Texas, endorsed Crist immediately after he entered the race against Rubio. 

Jesmer said Cornyn tried calling Crist to convey the message that he should drop out if he thinks he can’t win the primary, but Crist didn’t return the call. Jesmer also told the consultants that if Crist runs as an independent candidate, “we will support Marco Rubio in any way possible." 

“If any of you have influence with Governor Crist, we hope you will call his campaign and encourage him to do the right thing,” Jesmer wrote. 

Crist must decide by April 30 if he will remain in the Republican primary or take his chances in the general election without a party. He cannot switch after the primary. His campaign did not immediately respond to e-mails and phone messages seeking comment Monday. 

A year ago, a Quinnipiac University poll showed Crist ahead of Rubio by 46 percentage points. Last week the same poll showed Rubio ahead by 23 percentage points. U.S. Rep. Kendrick Meek is the leading Democrat in the race. 

Former Massachusetts Gov. Mitt Romney campaigned with Rubio in Tampa on Monday and had a similar message to Jesmer’s, saying Crist should either drop out of the race altogether or stay in the GOP primary. Romney said he expects Crist to “do the right thing." 

Romney is often mentioned as a potential 2012 presidential candidate. By backing Rubio, a favorite of conservatives, he could help endear himself to Republican voters who were uncomfortable with his moderate stands on abortion and gay rights when he ran for office in Massachusetts. 

In an interview after the event, Rubio declined to issue the same challenge as Romney, saying the reason he is running will not change no matter who is in the race. 

“I think we need to send someone to Washington who will stand up to the Obama agenda and offer an alternative, and both Kendrick Meek and Charlie Crist, I think, to one extent or another, would support the Obama agenda,” Rubio said. He said he hadn’t thought about how his campaign strategy would change with Crist running as an independent. 

Crist endorsed Sen. John McCain over Romney just days ahead of Florida’s 2008 GOP presidential primary, and some political observers believe that was enough to give McCain the win, which he used to build momentum and capture the nomination. 

Two other 2008 presidential candidates – former New York Mayor Rudy Giuliani and former Arkansas Gov. Mike Huckabee – have endorsed Rubio too. Giuliani was also counting on a Florida victory during the 2008 campaign and now says Crist backed out of a promised endorsement. 

Romney said he respects Crist, but Rubio’s “proven record of conservative, principled and idea-driven leadership is what Florida needs now." 

Romney’s PAC is contributing the maximum $5,000 allowed to Rubio’s campaign. In 2006, Romney flew to Tallahassee as head of the Republican Governors Association with a $1 million check to help Crist’s run for governor. 

Crist, Rubio and Meek are running to fill the seat held by George LeMieux, Crist’s former chief of staff. Crist appointed him after Mel Martinez resigned before completing his first term, saying he wanted to spend more time with his family.