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Lt. Gov. Jay Dardenne drew a stinging rebuke from Republican Party leaders after he decided to cross party lines and endorse Democrat John Bel Edwards in the Louisiana governor’s race Thursday.

Louisiana GOP chairman Roger Villere called him “the Nick Saban of Louisiana politics” — a personal dig comparing Dardenne, whose political career started in LSU’s student government, to the LSU-turned-Alabama football coach whose name has become synonymous with “traitor.”

Republican National Committee Chairman Reince Priebus called Dardenne’s decision to back Edwards over Republican U.S. Sen. David Vitter an “act of betrayal to the Republican Party.”

But Dardenne, who announced his endorsement on LSU’s campus, largely waved it off and said he knew what was coming.

“I’m all about Louisiana and what’s best for Louisiana,” Dardenne said. “John Bel has the best chance of unifying the state.”

Voters will decide between Edwards and Vitter in a Nov. 21 runoff election. Early voting starts Saturday.

Recent polls have shown Edwards with a double-digit lead over Vitter, once the presumptive frontrunner in the race.

And Dardenne’s endorsement could sway some Republicans who remain on the fence to back Edwards.

Dardenne came in fourth place in the Oct. 24 primary with about 15 percent of the vote. Republican Scott Angelle, who came in third closely behind Vitter, took about 19 percent. Angelle hasn’t endorsed either candidate, but both camps have been trying to gain his support, just as both tried for Dardenne’s backing. (A group of Angelle supporters has planned a fundraiser for Edwards in Lafayette on Friday.)

The three major Republicans engaged in a bitter battle that included several Vitter-backed attacks on Dardenne and Angelle that played out on TV and in public forums and debates.

Vitter’s campaign released a brief statement Thursday on Dardenne’s decision to endorse his Democratic rival.

“We’re very excited about our campaign and the tens of thousands of conservative Louisiana voters who have jumped on board in the past week, including so many that voted for Jay,” it said. “We wish Jay and his family the best.”

But Priebus and Villere sent Dardenne a tersely-worded letter.

“You cannot claim to be a conservative fighter for Louisiana principles and publically (sic) endorse an Obama liberal like Mr. Edwards,” they wrote in the joint letter.

Villere, in a separate statement, compared Dardenne to Saban’s betrayal of LSU. LSU and Alabama face each other on the football field Saturday.

“After decades of using the Republican Party and its members for his benefit, Jay has decided to end his political career by supporting a candidate who opposes every public policy position that he once espoused,” he said. “It is sad that Jay allowed his personal feelings to cause him to betray his party and state.”

Meanwhile, The Republican Governors Association, America Rising political action committee and others supporting Vitter rushed to point out that just a few weeks ago, Dardenne criticized Edwards as making “empty promises” and warned he would be ineffective as governor.

After the news conference Thursday, Dardenne said he felt comfortable backing Edwards, in part, because the Louisiana Legislature is controlled by Republicans.

“I don’t believe he has any intent of undoing what we’re doing,” he said.

Both Dardenne and Edwards said that Dardenne had not been promised anything in return for his backing, though Vitter’s supporters have speculated that Dardenne is angling for an appointment in Edwards’ administration, if elected. A Change.org petition has been set up online anonymously advocating for Dardenne to be named commissioner of administration — a powerful post in the governor’s administration.

Edwards said Dardenne’s endorsement was significant to him on a personal level, not just his campaign.

“I’m just proud to have it,” he said. “He’s always worked for the people of Louisiana.”

“I’m the one candidate left in this race who can bring people together,” he said.

Vitter earlier this week won the endorsement of former Gov. Mike Foster. Just hours after Dardenne announced his endorsement with Edwards at his side on LSU’s campus, Vitter's campaign announced that he had been endorsed by the Louisiana Home Builders Association, ABC Merit PAC and ABC Pelican PAC.

Editor's note: This story originally reported Edwards' campaign announced he had been endorsed by the Louisiana Home Builders Association, ABC Merit PAC and ABC Pelican PAC. Those endorsements are for Vitter's campaign.

Follow Elizabeth Crisp on Twitter @elizabethcrisp. For more coverage of Louisiana state government and politics, follow our Politics blog at http://blogs.theadvocate.com/politicsblog .