"Mark Pryor has changed. Now it's time to change Senators," the ad concludes.
Pryor, who many expect will face Rep. Tom Cotton (R-Ark.) this fall, is likely in for a rough fight this election. Strategists on both sides of the aisle say he's the incumbent who faces the toughest reelection battle, and outside groups have already been on the air for months seeking to tie him to President Obama.