Sen. David Vitter's (R-La.) lead on Rep. Charlie Melancon (D-La.) has grown to 18 points, according to a new Southern Media Research and Opininon Research poll.

The pollster last surveyed the race in October, when Vitter led 48-36. The lead, since then, has grown to 49-31.

Melancon has room to grown; he is still unknown to 41 percent of voters, compared to just 10 percent for Vitter. Vitter's approval rating, though, is solid, at 54 percent positive and 36 percent negative.

The survey was conducted for Baton Rouge businessman Lane Grigsby, a Republican donor who has contributed to Vitter. Grigsby also paid for the last poll.