What Happens When a Former President Refuses a Subpoena?

There's not much of a chance that if this goes up the Supreme Court, they're going to make him go testify. As we've seen with Steve Bannon, you can't just refuse to show up necessarily. It's never been decided, though, what happens when a former president resists a congressional subpoena. But one thing that's clear is that this subpoena was written almost like an indictment.