There is a new and significant sign today that the Obama campaign is facing a headwind. While the re-elect effort itself and the DNC have so far outraised the Republicans, the Democratic super PACs, or independent expenditures, have shown anemic results. Priorities USA, which is the unofficial Obama PAC, and the one with the closest former ties to the White House, raised only $5.2 million in the first half of the year, reports Politico's Kenneth Vogel. That is less than some Senate campaigns and is dwarfed by the main Republican super PACs, such as Karl Rove's American Crossroads, which had raised $24.5 million by early September. Crossroads has decided to double its initial goal of raising $120 million through the end of 2012, and privately, I'm sure, has a much more ambitious number in mind.

What's going on and what does it mean?

First, President Obama's campaign and the DNC have a vast, existing universe of small donors to draw upon, combined with "bundlers" who will help them to raise money in larger chunks. So far, that operation is going well. But campaigns have significant overhead. For them, it costs a lot of money to raise money. The Obama campaign, for example, has to pay for transporting the president to various fundraisers – and Air Force One isn't exactly Southwest. Then, there are staffers to pay, offices to open, etc. Which doesn't leave much money for trying to engage voters.

The super PACs, meanwhile, are little more than mailboxes, e-mail addresses and consultants -- whose compensation, by the way, is almost always a  relatively low percentage of money raised. So super PACs have minimal overhead, coupled with the ability to raise money in huge chunks.  These groups don’t care about small donors; they are targeting people who can write checks of $100,000 and up. And because of their economics, the super PACs put almost all the money they raise directly into television or GOTV efforts.

The super PAC problem may have been predictable given discontent with the president. Large donors on the Democratic side tend to be ideological, and some believe the president has been too accommodating to Republican interests. Nonetheless, it is potentially crippling to the president's electoral prospects. 

Bill Clinton's and George W. Bush's re-elections depended on massive fundraising advantages to define their opponents negatively before Bob Dole or John Kerry knew what hit them. Indeed, a central strategic assumption of this race has been that the Obama team and its allies would launch a massive negative advertising blitz on the eventual Republican nominee before he or she has even had a chance to celebrate. That advantage is now in jeopardy.