HEATING UP IN FLORIDA…. The Republicans’ Senate primary in Florida — pitting Gov. Charlie Crist against former state House Speaker Marco Rubio — has become something of a proxy for the larger fight within the GOP. The struggle pits conservative Republicans against very conservative Republicans.

And by all indications, the latter contingent is winning.

Rubio leads by just three percentage points — 47-44 — which is well within the error margin of the Quinnipiac University poll.

Crist has a large cash advantage over Rubio and ample time to catch up before the Aug. 24 primary. Yet the trend of Rubio’s rise and Crist’s fall is stark and troubling for the governor, who once looked like he would waltz into the Senate.

In October, Crist led 50-35 percent. In August, Crist’s lead was even bigger (55-26) and in June the race looked like Crist would blow out Rubio by 54-23 percent.

“Who would have thunk it? A former state lawmaker virtually unknown outside of his South Florida home whose challenge to an exceedingly popular sitting governor for a U.S. Senate nomination had many insiders scratching their heads. He enters the race 31 points behind and seven months later sneaks into the lead,” said Peter Brown, assistant director of the Connecticut-based Quinnipiac University Polling Institute.

In match-ups against the leading Democrat, Rep. Kendrick Meek of Miami, Rubio leads by nine and Crist leads by 14 — in part because Crist enjoys relatively stronger support among independents and some Florida Dems.

It’s hard not to wonder if this race may yet take some unexpected twists. Meek became the Democratic frontrunner because no one else in the party wanted to take on Crist, who once looked unbeatable. Now that it appears likely that the right-wing Rubio will win the primary, is there a chance we’ll see the Democratic race shift at the last minute?

Also note, Daily Kos fielded a poll in late November and found that Crist would be in a very strong position to win the Senate seat — if he switches parties and runs as a Democrat. It prompted Markos to conclude that Crist’s “cleanest path to a Senate seat” is “switching parties and making an earnest transition on the issues.”

For the record, there hasn’t been so much as a hint from Crist about a willingness to switch. On the contrary, he’s been trying to convince Florida Republicans that he’s really more conservative than he seems (which, incidentally, is what Arlen Specter did before he realized it was a lost cause and became a Dem). For that matter, it’s not at all clear if Florida Democrats would accept Crist with open arms.

But it’s fun to ponder, I suppose.

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Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.