The only Republican who would immediately force a tough race with Franken is the man he narrowly beat in 2008, former Sen. Norm Coleman (R-Minn.). But Coleman has ruled out a Senate bid, and is said to be eyeing a run for governor instead.

The automated poll of 1,065 Minnesota registered voters was conducted from Jan. 18-20 and had a margin of error of 3.0 percentage points.