When your best defense is saying, it's a political witch hunt, you're fucked.

[dpibel]

8. But Congress can't enforce its own subpoena

Congress has no ability (other than the possibility of inherent contempt) to enforce a subpoena. It can ask the AG to enforce, and, as demonstrated by the Meadows case, the AG may or may not.

A court, OTOH, has at its immediate disposal the constabulary and the jail. A judge can instruct the bailiff to march you straight from the courtroom to a cell if you're sufficiently contemptuous.

IOW, a one-step process for a judicial subpoena; a two-step one for Congressional.

There are assuredly complexities in the Graham subpoena, not least of which is how much compulsion a court can exercise over a nonresident witness. I don't know the answer to that.