Senate Democrats on Thursday used a procedural device to block a vote on a resolution disapproving the Iran nuclear agreement, saving President Obama the discomfiture of having to veto a measure of opposition to a signature foreign policy initiative. “Yes!,” came an exclamation as the number of votes to prevent the disapproval motion from moving forward reached the target of 41 required by Iran deal supporters. Sen. Dianne Feinstein (D-Calif.) punched the air with both fists in evident delight at the outcome. The final vote was 58-42, with Republicans—joined by Democratic Sens. Chuck Schumer of New York, Robert Menendez of...