Today’s Quinnipiac poll doesn’t give Marco Rubio very much good news.  Since the last poll seven weeks ago, Crist’s support has fallen back slightly, but he still maintains a five-point edge over Rubio among registered voters.  That lead extends to six points if Kendrick Meek wins the Democratic nomination, but Quinnipiac warns Crist that either Democrat could become a problem if Democratic voters start coming home to the party:

In the Senate race, Crist’s lead is based on getting half the independent voters, about 20 percent of Republicans and about 40 percent of Democrats. His 53 – 37 percent voter approval of his job as Governor probably is a factor in his lead.

Crist’s margin in the general election matchups compare to a 37 – 33 – 17 percent lead with Meek in the race and 40 – 33 – 14 percent with Greene running in a June 9 poll.

“There has been little movement in the Senate race over the past two months. Gov. Charlie Crist’s small lead comes as neither Democrat breaks 20 percent in the trial heats. If that were to be the case in November, Gov. Crist would have a very good chance to win. But if the Democratic nominee can move into the mid-to-high 20s, Crist’s chances decrease substantially,” said Peter A. Brown, assistant director of the Quinnipiac University Polling Institute.

Crist also has a significant edge on name recognition in Florida, which will certainly change after the primaries. When that happens, those numbers may start moving on their own:

Florida voters give Crist a 49 – 35 percent favorability rating with 13 percent who say they don’t know enough about him to form an opinion. Rubio has a 35 – 24 percent favorability, with 38 percent who don’t know enough about him. The “don’t know enough” score for Meek and Green is 64 percent each.

“At this point, Crist’s edge is in name identification. When those numbers even out, as they will to a large degree, we’ll have a better picture of how the race stands,” Brown said.

The big risk for Crist is keeping Democrats on board. Republicans may start cheering for Jeff Greene, the self-funding billionaire challenging Kendrick Meek for the nomination.  Meek has utterly failed to connect to voters statewide despite being a Congressman for more than seven years from the Miami area.

Greene, on the other hand, has bottomless pockets and would be expected to run a big campaign.  He has more upside with Democrats and may be seen as more moderate than Meek, especially on economic matters.  That would directly erode Crist’s standing with the moderate Democrats he has been attracting, and would create a fight on the center-Left.  Rubio could then win the center and the Right and beat both in a three-way race.

Bear in mind, also, that Quinnipiac polls registered voters, not likely voters, as Rasmussen does.  The latter model is more predictive — and likely voters are presumably more interested in the race, which means they know the candidates better.  I’d expect the Q-poll numbers to drift towards Rasmussen’s than the other way around.