From a profile of Ted Cruz in GQ:

“When I was Texas solicitor general, I did every argument in these [ostrich-skin cowboy]  boots. The one court that I was not willing to wear them in was the U.S. Supreme Court, and it was because my former boss and dear friend William Rehnquist was still chief justice. He and I were very close—he was a wonderful man—but he was very much a stickler for attire.” 

It was only after Rehnquist died that Cruz felt comfortable wearing his cowboy boots in the Supreme Court—and only then because John Roberts (“a friend for many years”) blessed it. “I saw John shortly after his confirmation,” Cruz said, “and I guess I was feeling a little cheeky, because I took the opportunity to ask, ‘Mr. Chief Justice, do you have any views on the appropriateness of boots as footwear at oral argument?’ And Chief Justice Roberts chuckled and he said, ‘You know, Ted, if you’re representing the state of Texas, they’re not only appropriate, they’re required.’ “

Ostrich foot