Here is (to me) the key paragraph in the Journal's editorial:
The Obama campaign is now distancing itself from Acorn, claiming Mr. Obama never organized with it and has nothing to do with illegal voter registration. Yet it's disingenuous to channel cash into an operation with a history of fraud and then claim you're shocked to discover reports of fraud. As with Rev. Jeremiah Wright and William Ayers, Mr. Obama was happy to associate with Acorn when it suited his purposes. But now that he's on the brink of the Presidency, he wants to disavow his ties.