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.

Donald Trump and Elon Musk are spending a lot of time around each other these days. How strong is their friendship?

Trump said he wants his Cabinet to “keep good people” as he addressed sweeping government cuts – but he also warned that “we’re going to be watching.”