President Obama is famously disciplined – six weeks shy of his fiftieth birthday, and there isn’t an ounce of fat on the man – but a moment’s indulgence earlier this month, of the sort the Harvard-trained lawyer normally never allows himself, has provided his political foes the ammunition for one of their first coordinated attacks of the 2012 campaign.

The ill-advised moment came on June 13, as the president met with his Council on Jobs and Competitiveness in Durham, North Carolina.  Discussing the public works projects that have been funded by the massive stimulus program he signed into law back in February 2009, the president quipped onstage: “Shovel-ready was not as shovel-ready as we expected.”

The implication was that his own administration’s promises of swift progress on infrastructure have proved overly optimistic.

Flash-forward to today, and the debut of a new attack ad sponsored by Crossroads GPS, the 501-C-4 group that counts Karl Rove, who is also a Fox News contributor, as a driving force and which does not have to disclose its donors.

Along with its 527 cousin, American Crossroads –  which does have to disclose its donors, but can engage in different kinds of political messaging – the group raised $71 million in 2010, and is credited with helping the G.O.P. reclaim control of the House of Representatives.

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“Obama's 830 billion dollar stimulus failed,” intones a female announcer in the new spot. (Pause here to note the little-noted phenomenon that modern political attack ads are almost invariably narrated by women – under the presumed theory that the viewers will regard women as more trustworthy, and not imagine female voice-over artists to be as pliable and mercenary as male ones.)

The next shot shows the president eliciting chuckles with his line in Durham: “Shovel-ready was not as shovel-ready as we expected.”  Then the narrator returns, with her stentorian tone of disapproval, to say: “Fourteen million out of work.  America drowning in debt.  It's time to take away Obama's blank check.”

The 30-second spot heralds Crossroads’ first major ad-buy of the 2012 cycle: estimated at $5 million and said to represent only one-quarter of the total the group plans to spend purchasing TV time, for this and other spots, in ten battleground states over the next two weeks.

“My take is it was a very good and effective ad,” said Doug Schoen, the longtime Democratic pollster who is now a Fox News contributor.  “It suggests that [the 2012 cycle] is going to be a total brawl, because…you are going to see the Obama administration, or its supporters, responding in kind, with just as tough ads.”

Indeed, when G.O.P. presidential candidate Mitt Romney visited South Carolina last month, hoping to sway voters in what will be the South’s first Republican primary, there to greet him was an attack ad that ran on virtually every newscast in the state.  The screen alternates between two grainy, black-and-white images of the former Massachusetts governor, the better to portray him as a flip-flopper on the issue of Medicare funding, as the (female) narrator tsk-tsks: “With Mitt Romney, you have to wonder: Which page is he on today?”

That ad was the work of Priorities USA Action, the pro-Democrat Super PAC co-founded two months ago by Bill Burton, the former deputy press secretary in the Obama White House, and Sean Sweeney, a top aide to Rahm Emanuel when the latter was White House chief of staff.  Burton hopes to raise $100 million on behalf of Democratic candidates and causes.

“We want to be a countervailing force to them,” Burton told Fox News in a telephone interview on Monday, referring to the Crossroads groups and another, similar outfit: Americans for Prosperity, funded by the conservative Koch brothers, proprietors of Koch Industries.  “We wouldn’t exist if they didn’t exist.”

Like Rove, Burton is joined in the fray by like-minded allies.  A pro-Democrat Super PAC called House Majority unveiled radio and cable TV ads on Monday targeting eight G.O.P. congressmen for their stands on Medicare and the extension of the Bush-era tax cuts.

All of this activity, of course, is founded on the belief that advertising across various media platforms does help shape the outcomes of elections.  It is such an article of faith that it goes unchallenged by the savviest political professionals, and serves as the centripetal force around which swirls hundreds of millions of dollars.  “Even bad ads have a real impact,” Burton said.