Former Florida state Rep. Adam Hasner (R) is getting closer to running against Sen. Bill Nelson (D-Fla.). (Steve Cannon/ASSOCIATED PRESS)

Two sources confirm that well-known GOP lawyer Cleta Mitchell has been advising Hasner since the effort launched earlier this month. Since then, the former state legislator has been quietly raising money and testing support among grassroots leaders while gearing up for a likely bid.

State Senate President Mike Haridopolos is already running. Former Sen. George LeMieux is expected to add his name to the mix, and Rep. Connie Mack and attorney Will McBride (a 2006 candidate for Nelson’s seat) are also looking at the race. (The field got a little smaller this weekend when wealthy Rep. Vern Buchanan (R-Fla.) suggested he is likely to stay put in the House.)

With the primary field in a state of flux, the name of a little-known state representative could get lost in the shuffle. But Hasner’s supporters says he will be able to bring together the kind of broad conservative support that characterized now-Sen. Marco Rubio’s rapid ascent in 2010.

At just 41 years old and with a stint in House GOP leadership behind him, the “Hasner as Rubio” comparisons are relatively easy to draw. Hasner was actually drafted into state House leadership by Rubio, a former state House speaker, and the two men are close, with Hasner supporting Rubio’s Senate primary campaign against then-Gov. Charlie Crist before many other conservatives jumped on board in 2010.

Hasner’s supporters think there’s another parallel between 2010 and 2012: a weak GOP field. While Crist labored under his support of President Obama’s stimulus plan in 2010, the candidates mentioned above have their own liabilities heading into 2012.

Haridopolos has fallen victim to a series of negative headlines since launching his campaign – including getting paid $152,000 for a book that was never published and being admonished for incomplete financial disclosure statements – while LeMieux can be closely tied to Crist as his former chief and chief political capo. (Crist appointed LeMieux to the Senate in 2009 to fill the vacancy created by Republican Sen. Mel Martinez’s resignation.)

Citing the vacuum in the GOP primary, respected Florida political reporter Adam Smith recently remarked that Hasner “could be the one to watch.” (Check out Smith’s profile of Hasner from January.) And Smith isn’t the only one suggesting Hasner has a niche in a field full of lackluster candidates.

Haridopolos takes issue with that characterization; “I think my strength will be showing during the legislative session,” he told The Fix. “A key to my campaign success is going to be how well the (state) Senate runs this year.”

Hasner considered a run for Congress and state attorney general last year, when he was term-limited out of the state House, but his wife was busy running the California gubernatorial campaign of Republican former eBay CEO Meg Whitman — a job for which Jillian Hasner was reportedly paid nearly $1 million.

His biggest potential problem will be fundraising. He begins his campaign from a significantly smaller perch than Haridopolos – much like Rubio did – and will have to build toward the big money over time. (Hasner’s “testing the waters” phase does not require a candidate to file with the Federal Election Commission, but any contributions received during this period are subject to FEC limits and would need to be disclosed if Hasner decides to run.)

Democrats say Hasner has a history of being “hot-headed,” and the state party began a campaign against “Hothead Hasner” when it looked like he might run for major office last cycle.

Florida is a swing state, and Nelson’s personal approval ratings have suffered alongside those of many incumbent senators. A recent Quinnipiac University poll found the senator’s approval at 45 percent and his disapproval at 21 percent. Just 43 percent of voters said he deserves another term.

He won a second term in 2006 with 60 percent of the vote after Rep. Katherine Harris, to the chagrin of establishment Republicans, ran away with the party’s nomination.