https://slate.com/news-and-politics/2020/02/dc-circuit-don-mcgahn-defy-subpoena.html
"By refusing the invitation to check an imperial executive, the panel just established the ongoing reality of an imperial executive. The decision can still be appealed to the full court or the Supreme Court. But barring a reversal, Congress may need to get creative. As an alternative, Judge Griffith suggested Congress order the Sergeant-at-Arms to arrest and detain their desired witnesses."