In Louisiana, Landrieu still has only about a 1-in-3 chance of winning even when her incumbent status is included. Her polling at this point isn’t good enough for incumbency to put her over the top.

In the closest races, however, incumbency may very well turn a loser into a winner.

Pryor’s chances of winning dropped from 58 percent with just Senate polling to 40 percent with early Senate polling and the president’s approval rating in his state. Add in his incumbency advantage, and Pryor has a 45 percent chance of winning.

Likewise, Democratic Sen. Mark Udall’s chances in Colorado climb back over 50 percent when we account for the fact that he is the incumbent.