Sen. Marco Rubio's (R) popularity is on the decline in Florida, a new poll showed, while Democrats have a small advantage over Republicans in the state's congressional races.

Just 40 percent of Florida voters now say they approve of Rubio, according to the poll released Tuesday by Democratic firm Public Policy Polling. That's down from 44 percent in September.

His disapproval ratings have also climbed steadily in every PPP poll since March, when 31 percent disapproved. In November, 40 percent said they disapproved.

The figures still mean Rubio is substantially more popular than member of Congress on average. But with less than half of voters in his state giving an approving nod, Rubio might be a less appealing candidate for those seeking to add his name to a presidential ticket.

Rubio, who is not up for reelection in 2012, has said he will not be the vice-presidential nominee, but that hasn't stopped many Republicans from continuing to float his name as the party's best choice to pair up with their presidential pick.

Democrats also have a 6-point advantage over Republicans in a generic ballot, where voters are asked to pick which party they would like to represent them in Congress, without specific politician names attached.

The poll of 700 Florida voters was conducted Nov. 28-Dec. 1 using automated telephone interviews and had a margin of error of plus or minus 3.7 percentage points.