Even before Marco Rubio decided to run for the White House, it looked like Florida Republicans had more or less settled on a front-runner to succeed him in the Senate, state CFO Jeff Atwater. But Atwater's decision to bail on the race—as surprising as Rubio's move was unsurprising—has left the GOP field wide, wide open. To help you keep the picture in focus, Jeff Singer has run down the most likely candidates , along with their strengths and weaknesses, while Daniel Donner (the artist formerly known as dreaminonempty) has assembled the scorecard above.

We also have some new polling data, courtesy Mason-Dixon, that confirms how fluid the fight for the Republican nomination is. Here's where things stand in a hypothetical kitchen-sink scenario:

Bill McCollum: 20

David Jolly: 8

Vern Buchanan: 7

Tom Rooney: 5

Ron DeSantis: 4

Carlos Lopez-Cantera: 4

George Lemieux: 3

Don Gaetz: 1

Undecided: 48

McCollum's perch at the top is entirely a function of his name recognition: Thanks to his service as attorney general and his multiple statewide runs (most recently for governor in 2010), only a quarter of the state is unfamiliar with him. Everyone else, on the other hand, is almost entirely unknown, and McCollum, who is 70, doesn't even seem particularly likely to run. There are also three potential names Mason-Dixon didn't include (Reps. Curt Clawson, Jeff Miller, and Dennis Ross), and Rooney's already said no, so it'll be a while yet before we can get an accurate read on this primary—though it's a safe bet that the final roster won't be quite so large.

Meanwhile, it turns out that Lopez-Cantera won't be able to count on support from his current boss, something that had at one point seemed likely. Gov. Rick Scott just announced that he won't take sides in the primary, though he did offer some praise for his number two. Lopez-Cantera will be irrevocably associated with Scott whether he wants to be or not, so it's not like seeking help from the governor would realistically affect Lopez-Cantera's image. Now, it seems, he'll have to deal with the worst of both worlds: No overt backing from the wealthy Scott, but blame for every unpopular decision he makes.

On the Democratic side, we still don't know whether we'll have a contested nomination battle, though Alan Grayson has said he thinks he'll "probably" run against fellow Rep. Patrick Murphy, the only candidate in the race so far. Interestingly, Grayson would start off behind Murphy, 23-14, even though he's better-known. However, Murphy has a near-spotless 18-2 favorability rating while Grayson sits at 13-14, suggesting that the old adage about how there's no such thing as bad publicity may not be true. (However, an earlier PPP poll had Grayson ahead 22-21.)

Mason-Dixon hasn't released general election numbers, but previous surveys from both PPP and Quinnipiac show that the general is just as uncertain as both primaries. No matter what, though, Florida, as it so often does, will prove a crucial battleground—in this case, for control of the Senate—and as always, we'll be keeping close tabs on all developments at Daily Kos Elections.