Mr. Musk is fundamentally a creature of Silicon Valley, a scene that initiated an entire revolution in power dressing. The young masters of that universe dressed down to show that they were members of a new elite — one that refused to dress like the grown-ups they were about to topple. It was the defeat of the suit by the T-shirt.

Trump told reporters he would write a check for the car, which retails for roughly $80,000, and leave it at the White House so his staff can drive it. The president also said he hopes his purchase will boost Tesla,