The Crossroads ad marks a departure for it and most other outside political groups. Until now, they have spent most of their money on such themes as criticizing Mr. Obama for the rising federal deficit. But the new ad is the first from Crossroads to mention Mr. Romney explicitly, and in defending him it serves a role that candidates traditionally have filled themselves.
The ad underscores an important feature of how the race is being financed. Outside GOP committees, along with Mr. Romney's campaign, are raising more money than their opponent, and plan to outspend Democrats this week on TV by about 2.5-to-1, according to figures provided by Democratic and Republican media-tracking sources.
But in spending by the campaigns themselves, Mr. Obama is putting more money into TV ads currently. Mr. Obama will spend more than $9.4 million on ads in the coming week, compared with $6.6 million by Mr. Romney. Since the unofficial start of the general election in mid-April, Mr. Obama has outspent Mr. Romney by about 3 to 1.
Campaign officials have suggested that, in part, the disparity is due to the fact that much of Mr. Romney's money was raised under rules that limit its use to the general election, once he becomes the nominee. Mr. Obama is bound by the same restriction, but only Mr. Romney faced an expensive primary campaign that ate into money he was raising.
The campaign won't say what fraction of Mr. Romney's cash is so encumbered.