From this important NYT report:

The White House has been focused on passing the so-called Disclose Act, proposed legislation that would place new limits on interest groups trying to influence elections by restricting corporate spending in some instances and requiring new levels of disclosure over all.
But, speaking on the condition of anonymity because they did not want to engage in a public dialogue on the matter when they were so focused on Election Day, strategists for Mr. Obama said they were intent on avoiding a situation in which they would have no answer to millions of dollars — if not tens of millions — in advertisements from groups like Crossroads and Crossroads GPS.