Obama campaign senior adviser David Axelrod this week blamed Illinois’ low primary turnout on the barrage of negative ads the GOP candidates have unleashed on each other.

He was correct about the negativity of the 2012 campaign – but the candidates’ ads are only part of the picture.

According to The Post’s Mad Money campaign ad tracker, the ads being aired by the super PACs supporting the GOP presidential candidates are far more negative than the ones being aired by the White House hopefuls themselves.

All in all, an average of 77 percent of the ads run by the super PACs supporting the four GOP candidates have been negative.

By comparison, an average of 54 percent of all ads aired by the four candidates’ campaigns have been negative ones.

The most negative super PAC so far: the pro-Romney group Restore Our Future. Ninety-two percent of the ads aired by the super PAC have been negative.

(It’s also the biggest spender by far, dropping more than $24 million on the GOP race to date.)

The pro-Santorum Red, White and Blue Fund has been overwhelmingly negative on the airwaves, too – 84 percent of its ads have been negative – while the pro-Gingrich and pro-Paul super PACs have been less so (67 percent and 65 percent, respectively).

Most of the campaigns have aired more negative ads than positive ones, with the exception of Gingrich. Fifty-three percent of the Romney camp’s ads have been negative. The number is 61 percent for Santorum, 53 percent for Paul and 47 percent for Gingrich.

That doesn’t mean the candidates haven’t been negative – particularly when it comes to their campaign-trail attacks. It just means the super PACs backing them have been even more focused on tearing down the rest of the GOP field than the candidates themselves have been.

Here’s a closer look at today on the trail (Courtesy of candidate schedules and the PBS NewsHour Political Calendar; all times Eastern):

8 a.m.: Mitt Romney holds a fundraiser at the Hyatt Regency in downtown Washington.

11 a.m.: Rick Santorum addresses the USAA in San Antonio, Texas.

1 p.m.: Newt Gingrich holds a meet-and-greet in Houma, La.

9 p.m.: Newt Gingrich attends a tea party forum in Baton Rouge, La.