https://news.ycombinator.com/item?id=43000640 is an article about Vance saying it, like, two days ago. (You're going to have to have showdead on to see the link, though.)

And he didn't quite say that the judiciary can't check the executive. He said that the judiciary can't check the "legitimate power" of the executive. (Of course, that completely misses that the judiciary checks the executive precisely by ruling that something is outside the legitimate power of the executive...)