Florida Gov. Charlie Crist is “irreparably” damaging himself by choosing to run as an Independent for the Senate, according to the chairman of the National Republican Senatorial Committee.

Crist, a Florida Republican, is expected to withdraw from the race for the GOP Senate nomination and announce his Independent candidacy during a press conference Thursday evening in St. Petersburg.

Sen. John CornynJohn CornynMcConnell names Senate GOP tax conferees Air Force makes criminal reporting changes after Texas massacre We need a better pathway for allowing civilians to move guns across state lines MORE (R-Texas) said Thursday that Republicans encouraged Crist to either stay in the GOP primary or drop out and run again in 2012 against Sen. Bill NelsonClarence (Bill) William NelsonOvernight Health Care: Ryan's office warns he wasn't part of ObamaCare deal | House conservatives push for mandate repeal in final tax bill | Dem wants probe into CVS-Aetna merger Ryan's office warning he wasn't part of deal on ObamaCare: source Overnight Health Care: Funding bill could provide help for children's health program | Questions for CVS-Aetna deal | Collins doubles funding ask for ObamaCare bill MORE (D-Fla.).

“Staying in the primary and dropping out and running in ’12 are preferable, much more preferable, than running as Independent,” Cornyn said Thursday at a breakfast sponsored by the Christian Science Monitor.

“His future electoral prospects are irreparably damaged by his deciding now to run as an Independent.”

Cornyn admitted he hasn’t been able to speak with the governor directly about his decision. “I’ve played a lot of phone tag with him,” Cornyn said. “I’ve sort of given up out of frustration.

“But I know that message has been communicated, both by my staff and by other people close to the governor,” Cornyn said. “He’s a smart guy he can see what his choices are.”

Should the governor switch his party affiliation, “it will end our support and we will throw our support enthusiastically behind the Republican nominee, Marco RubioMarco Antonio RubioRyan pledges 'entitlement reform' in 2018 Richard Gere welcomes lawmakers' words of support for Tibet Dem lawmaker gives McConnell's tax reform op-ed a failing grade MORE,” Cornyn said.

Cornyn wouldn’t quantify the amount of money Crist would have to refund if he launches an Independent bid. But he did say he would request  Crist return the $10,000 his leadership PAC donated.

After Crist’s announcement, the primary is effectively over and Cornyn said the committee’s focus will turn to the Democrat in the race, Rep. Kendrick Meek (D-Fla.).

“Once we get by this drama of today, it’s going to be in essence a general election campaign and people are going to begin focusing on Kendrick Meek. A guy who voted for half-a-trillion-dollar cuts in Medicare, which Florida’s senior population may take a dim view of,” Cornyn said.

Cornyn said he initially tried to recruit former Florida Gov. Jeb Bush (R) to run for Senate before moving to recruit Crist.

“When Jeb Bush told me he wasn’t going to run, I looked around for the most popular Republican in the state, and it was pretty clear who that was,” he said.

“At the time we made the endorsement, Gov. Crist was one of the most popular governors in America. It’s been a breathtaking change of circumstance to see him now contemplating this course.”

Cornyn admitted the National Republican Senatorial Committee’s endorsement of Crist didn’t help his campaign.

“In this political environment, it’s not necessarily helpful for candidates running in states to have the national party chairman endorse them,” Cornyn noted. “That’s been a learning experience.”