Gov. Charlie Crist holds an early lead as an independent candidate in the U.S. Senate race, but his edge is a "proverbial house of cards," according to a new poll, because support from Democratic and black voters is unlikely to hold up through the Nov. 2 election.

The Mason-Dixon poll released Thursday found Crist receiving 38 percent of the vote, compared to 32 percent for the likely Republican nominee, former House Speaker Marco Rubio, and 19 percent for the leading Democratic contender, U.S. Rep. Kendrick Meek of Miami. Eleven percent are undecided.

More than half of Crist's supporters are Democrats, who overwhelmingly approve of his defection from the GOP and recent veto of a controversial teacher tenure bill. Against the lesser-known Miami congressman, who is black, Crist is favored by 19 percent of black voters and 48 percent of Democrats, according to the survey. Meek wins support from 68 percent of black voters and 36 percent of Democrats.

"It is very questionable whether or not these party and race numbers can hold up over the next six months unless the national Democratic Party and its leaders (including President Barack Obama) throw Meek under the bus," said Mason-Dixon pollster Brad Coker. "His strength among Democrats is likely a result of the fact that Meek is not known to 40 percent of state voters."

As an independent candidate, Crist will lack the fundraising and campaign volunteer networks built into the political party system.

Among Meek's Democratic rivals, former Miami Mayor Maurice Ferre received support from 4 percent of the voters, while the newest candidate in the race, real estate tycoon Jeff Greene, got 2 percent.

The poll of 625 likely voters conducted between Monday and Wednesday has a margin of error of plus or minus 4 percentage points.

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