This sort of ad is obligatory after a tough primary loaded with biting attacks from the nominee’s former opponents but rarely, I think, does it ever draw blood. Voters expect primary candidates to criticize each other. Usually it’s just noise. This one’s a little smarter than most examples of the genre because it has Santorum citing numbers about Romney’s economic record, which is a bit harder to shake off than the usual “my opponent stinks” blather that voters take for granted. Here’s the problem for the DNC, though: How many swing voters are apt to be swayed by a Santorum attack? Some sizable chunk of his GOP support was due simply to him being the last “Not Romney” standing. If I’m right that the voters who’ll decide the election won’t start paying attention until September, then those who stumble across this ad now will probably end up wondering, “Wait, who’s this guy again?” If you want to shank an opponent with criticism from someone in his own party, make sure that the critic is a hugely well-known figure. (Reagan did it right.) I think the ad is most useful as a preview of a line of attack that Obama himself will use against Romney to counter Mitt’s message on the economy. And you already know what Romney’s reply will be: “The reason our state’s economy lagged so much is because I had to work with a legislature full of Barack Obamas.” And on we go.

Incidentally, the big Romney/Santorum powwow finally happened today. Topics of discussion, allegedly:

John Brabender, who served as Santorum’s senior strategist during the campaign, said that when the former Pennsylvania senator sat down one-on-one with Romney, he wanted:

To discuss Santorum’s manufacturing plan, the keystone to the former candidate’s economic platform

Assurances that Romney would work to repeal President Obama’s health care law and that it would not be replaced with a plan containing a mandate

A commitment from the former Massachusetts governor to pursue “economic solutions that are pro-family”

Still no endorsement from Santorum, though. Is that coming this summer or will it be a convention-speech “surprise”? Exit question: Whither the Romney/Santorum ticket?