Former Florida Gov. Jeb Bush's sons plans to hold a private fundraiser for insurgent GOP Senate candidate Marco Rubio next month, Rubio told Fox News.

The active involvement of George P. Bush and Jeb Bush Jr. in the race raises the possibility that their father could endorse Rubio down the road and give his campaign added momentum against the GOP front-runner, Gov. Charlie Crist.

Jeb Bush, who has dismissed suggestions he'll support Rubio, still is enormously popular in the state, with a recent poll pegging his approval rating at 70 percent, outshining Crist. His backing could help Rubio offset Crist's considerable fundraising advantage.

Crist and Rubio, former speaker of the Florida House of Representatives, are facing off to fill the Senate seat vacated by former Sen. Mel Martinez.

The race has emerged as one of the pivotal battlegrounds between the more grassroots-driven conservative base of the GOP, represented by Rubio, and the more moderate wing, represented by Crist. That tension most recently flared in upstate New York's 23rd Congressional District election, in which Conservative Party candidate Doug Hoffman basically forced Republican candidate Dede Scozzafava out of the race. Hoffman ended up losing last week to Democrat Bill Owens.

Endorsements from high-profile Republicans like former Alaska Gov. Sarah Palin gave Hoffman late-in-the-game momentum in New York.

Though an endorsement from George W. Bush's brother is not assured in Florida, the former governor happens to be a mentor to Rubio, and he's had a well-known rivalry with Crist. His two sons holding the fundraiser in December are both personally close to Rubio.

On paper, Crist is still strong against Rubio. A Rasmussen poll released in late October showed Crist holding a 14-point lead over Rubio. But that was down from a 22-point lead in August.

Some GOP Hispanic analysts also have said that the Republican Party may be able to slow the bleeding of Hispanics to the Democratic Party with the help of Republicans like former Gov. Bush, who is fluent in Spanish and married to a Mexican woman, and Rubio, who is Cuban-American and also speaks Spanish.

Fox News' Serafin Gomez contributed to this report.