Sen. Bill Nelson had a double-digit lead over a handful of potential GOP challengers according to polling released Wednesday, but a closer look at the numbers suggests the Florida Democrat’s vulnerability heading into his 2012 re-election campaign.

The new survey from the Democratic firm Public Policy Polling tested Nelson, the only Democrat in Florida holding statewide office, against six potential GOP challengers. The incumbent led each Republican by 13 to 19 points, but the potential challengers kept him at 50 percent or below overall. That fact, coupled with Nelson’s favorability ratings, shows he might be in a weak position.

The two people who came closest to Nelson in hypothetical matchups actually aren’t running. Rep. Connie Mack IV, who announced last week that he will not enter the race, trailed with 34 percent to Nelson’s 47 percent. MSNBC host and former Rep. Joe Scarborough, who has said national Republicans tried to recruit him for the race but has ruled out a run, was behind with 32 percent to Nelson’s 45 percent.

The only announced candidate, state Senate President Mike Haridopolos, took 34 percent to Nelson’s 50 percent.

Others earned similar results. Former state House Majority Leader Adam Hasner, a favorite of grass-roots conservatives, earned 32 percent to Nelson’s 48 percent, former Sen. George LeMieux trailed 33 percent to 48 percent, and Wikipedia founder Jimmy Wales earned 28 percent to Nelson’s 47 percent.

PPP surveyed 500 Florida voters from Thursday to Sunday. The margin of error was 4.4 points.

There’s plenty of time for the numbers to change, especially given that the three most likely challengers aren’t widely known. PPP found that 65 percent to 87 percent of voters in the poll have no opinion of Haridopolos, Hasner and LeMieux.

Meanwhile, Nelson’s favorability ratings leave something to be desired.

Newly elected Republican Sen. Marco Rubio is slightly better known already and better liked, according to PPP, which found that 38 percent of voters approved of Nelson’s job performance, while 34 percent disapproved.

“Bill Nelson’s approval numbers make him look vulnerable but they might be a little deceiving,” PPP President Dean Debnam said in a statement. “Democrats don’t love him but they would still vote for him in a general election and his better than average support across party lines from Republicans means his eventual opponent will be starting from behind.”