Crist must decide by April 30 whether to remain in the GOP primary where former state House Speaker Marco Rubio is favored or pursue an independent bid. He has refused to shut the door on speculation he might bolt the party that helped him win races as Florida's attorney general and education commissioner before he became governor in 2006.
If the general election were held now, 32 percent of voters would favor Crist, compared with 30 percent for Rubio and 24 percent for the Democratic hopeful, U.S. Rep. Kendrick Meek, according to a survey of 1,250 registered voters taken April 8-13 by Quinnipiac University in Connecticut.
"The biggest threat to Crist's political career is the Republican primary," said Peter Brown, Quinnipiac's assistant polling director. "People overall think he is doing a good job as governor, but that doesn't mean Republicans think that he should be their U.S. senator."
Crist on Thursday vetoed a wide-ranging education bill favored by conservatives but unpopular with the public that would have made it easier to fire Florida teachers and link their pay to student test scores. Some political observers see the move as another signal that he will drop out of the primary and run as an independent.
In a poll of 497 registered Republicans, Rubio defeats Crist 56 percent to 33 percent in a head-to-head GOP matchup. In Quinnipiac's January poll, Rubio had a 47-44 lead.
Quinnipiac said its larger survey of voters in a three-way general election race had a margin of error of plus or minus 2.8 percentage points. The smaller sampling of only Republican voters had an error rate of plus or minus 4.4 percentage points.
Crist's biggest problem among Republicans is that they don't view him as conservative enough - the poll found 59 percent see Rubio as more consistently conservative, compared with 27 percent for Crist.
But what could hurt Crist in the primary could help in the general election. The poll found Crist would defeat Meek 48 percent to 34 percent, while Rubio would win with 42 percent of the vote to 38 percent for Meek, if that race were held now.
Quinnipiac's survey also showed Crist would fare better with independents than Meek or Rubio. In a three-way race, Crist had the support of 38 percent of those who called themselves independents compared with 29 percent for Rubio and 15 percent for Meek.
The numbers represent a dramatic reversal for the 53-year-old governor, who crushed former Insurance Commissioner Tom Gallagher in the 2006 GOP primary and then eased to a general election win by 7 percentage points over Democratic nominee Jim Davis.
Meek's biggest problem seems to be his anonymity. Only about a fourth of those surveyed had heard of the Miami congressman.
The three are vying to succeed Republican Mel Martinez, who left before his term ended. Crist appointed state Sen. George LeMieux to fill the seat temporarily.