Florida Gov. Charlie Crist doubles up State Rep. Marco Rubio in the Republican Senate primary, while more than half of Democratic voters don't yet have a favorite candidate, a new Quinnipiac survey finds. President Obama has a 58% approval rating (down 6 points from February), with Crist's slightly higher at 62% -- down 4 points from last month.

"Marco Rubio says there are many Florida Republicans who don't want Charlie Crist in the U.S. Senate," said Quinnipiac assistant director Peter Brown. "Depending on how you define the word 'many,' he might be correct. Unfortunately for Rubio at this stage, many, many, many more favor Crist."

Democrats tested were Reps. Kendrick Meek, Corrine Brown and Ron Klein.

GOP Primary
Crist 54
Rubio 23
Und 21

Dem Primary
Meek 18
Brown 12
Klein 8
Und 57