Are Obama and Democrats intervening in the Republican presidential race?

The hard-hitting ad above attacking Mitt Romney in the closing days of the Michigan primary wasn’t sponsored by Rick Santorum, or Newt Gingrich, or Ron Paul, or any of their Super PAC’s.

The ad was from Priorities USA, the Super PAC of the Obama campaign, and it was aired in the Detroit and Flint media markets, according to the publication The Hill.

The move raises the fascinating prospect that Obama and other Democrats may try and weigh in on Republican primaries to try and pick the guy they want to run against – presumably somebody besides Mitt Romney.

This kind of thing has happened before, right here in Philadelphia.

In the 1999 mayor’s race, Republican Sam Katz was running unopposed on the Republican side, while a heated five-way primary was underway among Democrats. Katz decided he wanted to run against John Street in the general, so he spent a hefty sum on TV ads attacking two of Street’s rivals – John White and Marty Weinberg.

It worked, sort of. Katz got the matchup he wanted, but lost narrowly to Street in November.

The size of the Obama PAC’s ad buy in Michigan wasn’t massive, but it wasn’t trivial either. According to Open Secrets (the wonderful site run by the Center for Responsive Politics), Priorities USA spent just under $200,000 attacking Mitt.

At the same time, exit polls suggest Democrats who participated in Michigan’s open primary (about a tenth of the those who voted ) went disproportionately for Santorum.

That was after Michael Moore told MSNBC that Democratic friends of his would vote for Santorum in something they called “Operation Hilarity,” and Democratic National Committee chair U.S. Rep. Debbie Wasserman Schultz denied there was any organized effort to get Democrats to vote for Republican candidates in Michigan.

What does it all mean? Democrats certainly aren’t going to pick the Republicans’ candidate if the elephant armies know what they want. But in a really close race, little things can matter – like Ralph Nader getting on the Florida ballot in 2000.