PRESIDENT OBAMA isn’t backing down from his campaign ad attacking Mitt Romney’s private equity firm, Bain Capital. Actually, “attack” may be too weak a description for a video that likens Bain to “a vampire” and depicts Mr. Romney as a plutocrat who callously destroyed hundreds of steel jobs for his own enrichment....

The president accepted $3.5 million in campaign donations from private equity executives in 2008, and additional dollars this time around, so it would have been awkward for him not to concede that private equity does “good work.” As for the ad’s depiction of job destruction, economists at the National Bureau of Economic Research found that firms restructured by private equity suffered net job losses over five years only 1 percent greater than other comparable companies.

Yet the minute Mr. Obama conceded those complications — admitted, in effect, that the private equity business, like most endeavors, involves tradeoffs, and that its benefits might be shared among more than a handful of fat cats — he undercut his distinction between “maximizing profit” and the common good. He also undercut his case against Mr. Romney, since Bain had its share of success stories on the former Massachusetts governor’s watch.

What we’re left with is a president who seems content to present an even-handed view of private equity at his news conferences while propounding a much more tendentious one in his campaign advertising. Pointing out that a business career hasn’t fully prepared Mr. Romney to be president, in other words, is a long way from suggesting that he’s a vampire.