Senator Mark Kelly, Democrat of Arizona, asked a federal judge to block the Trump administration from disciplining him for a video warning about illegal military orders.
A handful of Republicans joined Democrats to allow the measure to move forward, reflecting concerns in both parties about the administration’s strategy.
“Make no mistake: Bombing another nation’s capital and removing their president is an act of war, plain and simple,” Senator Rand Paul, Republican of Kentucky, said before the vote.
Republicans praised what they characterized as a narrow and well-executed plan, while Democrats expressed alarm, warning that the mission was vaguely defined.