Late Thursday night, two hours after it sent out President Barack Obama’s Friday schedule, the White House told reporters it was adding another event – a statement that he would give in the morning. Amid all the hoopla of the G-20 economic summit in Pittsburgh, there was scant indication the announcement would be dramatic. But behind the scenes, the Obama administration was furiously preparing for a major public intelligence disclosure that it had not planned to make: that the U.S. had known for years about a previously undisclosed clandestine nuclear enrichment facility Iran has been building since 2005 in...