Former Massachusetts Gov. Mitt Romney will endorse Marco Rubio over Gov. Charlie Crist in Florida’s Republican Senate primary more than two years after Crist helped crush Romney’s presidential aspirations by endorsing rival John McCain.

Romney plans to announce the endorsement Saturday and campaign with Rubio in Tampa today, according to a Romney adviser who asked to remain anonymous because the official announcement has not been made.

Romney is the third major 2008 presidential candidate to endorse Rubio. Former New York Mayor Rudy Giuliani and former Arkansas Gov. Mike Huckabee have also endorsed the former House speaker.

Crist and Rubio both sought Romney’s endorsement, the adviser said, but Romney believes Rubio has a stronger conservative record and is an idea-driven leader. Romney was also disappointed that Crist vetoed a teacher merit-pay bill this week that was a high priority for Republican lawmakers and former Gov. Jeb Bush.

Romney’s Political Action Committee is contributing the maximum $5,000 allowed to Rubio’s campaign.

The Rubio campaign said it would not comment on the endorsement until after it’s made.