The Mueller report confirms that the Obama administration, without evidence, turned the surveillance powers of the federal government against the presidential campaign of the party out of power. This historic abuse of executive authority was either approved by President Barack Obama or it was not. It’s time for Mr. Obama, who oddly receives few mentions in stories about his government’s spying on associates of the 2016 Trump campaign, to say what he knew and did not know about the targeting of his party’s opponents.

If he...