So why is Mr. Obama making such an incendiary charge without any evidence? One explanation is that he is laying the foundation for an alternative narrative—the Democrats lost because Chinese campaign cash allowed Republicans to steal the election. Another is that the president is trying to fire up his party’s base. But phony charges about campaign finance won’t appeal to independent voters, the true source of Democratic troubles this election.

A third possibility is that Mr. Obama hopes to intimidate contributors to the Chamber of Commerce, American Crossroads or Crossroads GPS. If so, his tactic is backfiring. Crossroads and GPS have raised more than $14 million since he began his assault last week, enabling them to become active in House races they weren’t targeting before.