TALLAHASSEE, Fla. (AP) — Former Gov. Charlie Crist, a former Republican, said Wednesday he is backing Democratic Sen. Bill Nelson's re-election campaign — a race in which he'll likely face the son of Crist's longtime political mentor.

Crist plans to attend a Nelson fundraiser Thursday at the home of his boss, lawyer John Morgan of the firm Morgan & Morgan. Former president Bill Clinton will be the featured speaker. Crist said he plans to donate money to Nelson's campaign and will vote for him in November.

Republican Connie Mack IV is the heavy favorite to win the Republican nomination during the Aug. 14 primary. Crist's failure decision not to support him is at odds with a long history he's had with the Macks that started when Crist worked to get Connie Mack III elected to the Senate in 1988. Throughout his career, Crist has called the elder Mack a mentor and has often quoted him. Both Macks were longtime Crist supporters.

But that changed when Crist ran for Senate in 2010 and dropped out of the Republican primary and instead ran as an independent. Mack III quit his role as Crist campaign chairman and both Macks withdrew their support and endorsed eventual victor Marco Rubio.

Crist said Nelson has been a good voice for Florida in Washington.

"Senator Nelson has been a friend, he and Grace both," Crist said, referring to Nelson's wife. "It's no knock on Connie."

Nelson's deputy campaign manager Marley Wilkes said, "The event will feature President Clinton and be attended many officials including the former governor. And we're glad to have all their support."

Mack's campaign responded to the news with three words.

"Is anyone surprised?" said Mack spokesman David James.

Supporting Nelson is sure to escalate speculation that Crist might try to return to politics as a Democrat. Crist served as a state senator before challenging popular Democratic Sen. Bob Graham in 1998. While he wasn't considered a serious threat to Graham, the experience helped him build a statewide political network and he won his next three statewide races for education commissioner, attorney general and governor. His name was often mentioned as a potential running mate for 2008 Republican presidential nominee John McCain.

Instead of seeking a second term as governor, Crist ran for Senate, at first seeking the Republican nomination and then dropping out of the primary after falling behind to Rubio. He later changed his voter registration to no party affiliation. His wife, Carole, switched her registration from Republican to Democrat last year.

Former Florida Democratic Party Chairman Scott Maddox said Crist supporting Nelson is "absolutely" a sign that he could become a Democrat soon.

"Charlie Crist was never a right wing Republican. He always had reasonable, moderate views and I think his support of Senator Nelson is right in line with that tact," Maddox said. "He did a lot of good things as governor and I think people appreciate that and he was never overly partisan."

And if he did make the switch, Maddox would welcome him.

"I would urge him to switch to the Democratic Party and I'd love to have him," he said. "There would be a lot of opportunity for Charlie Crist in the Democratic Party."


Follow Brendan Farrington on Twitter at https://twitter.com/bsfarrington