Simmering anger at the billionaire’s unchecked power spilled out in a remarkable Cabinet Room meeting. The president quickly moved to rein in Mr. Musk. Cabinet officials generally like the concept of what Elon Musk set out to do — reducing waste, fraud and abuse in government — but have been frustrated by the hacksaw approach to upending the government and the lack of consistent coordination. Marco Rubio was incensed. Here he was in the Cabinet Room of the White House, the secretary of state, seated beside the president and listening to a litany of attacks from the richest man in...