In his assertions of executive power to advance his agenda in an era of gridlock, President Obama has been largely on offense. But his latest battle with Congress not only left him on defense, it actually broke the gridlock. Against him. Mr. Obama’s abrupt decision to sign a compromise version of legislation on Iran that he had previously vowed to veto was a bruising retreat in his larger campaign to act without Congress’s getting in his way. In this case, partisanship gave way to rare consensus on Capitol Hill: Both sides agreed that he was wrong to cut them out. The White House tried to make the best of the setback, arguing that the bipartisan bill was less objectionable […]