The DSCC hits the Republican front-runner, former Governor and Agricultural Secretary Mike Johanns.
Kos likes it and thinks the "quitter" narrative is effective. I kind of think it's a cheap shot. Politicians of all stripes resign from their current post while running for the next one. This isn't aberrant behavior. It's typical -- even expected. When Joe Lieberman didn't resign from the Senate to run for Vice President, folks were really annoyed at him. A lot of the time, the argument is made that a Senator or Representative whose running for higher office can't concentrate on representing her district, and so should resign to focus on her campaign. This ad is the epitome of taking a neutral or beneficent act, saying it in a nasty voice, and hoping uninformed voters will take it badly.
It's not quite at the "I hear his sister is a thespian" level, but it's in that family.