One of the problems that congress has is that unless they can get the judicial system to order it, they have zero control over the executive branch. If the Justice Department will disregard the supenas coming out of the Congress then Congress has no way to force action on them on their own. This is the case we have right now. Barr is controlled by Trump and Barr controls the Justice Department. One would think that the US Marshals were strictly part of the DOJ but they are actually doing dual duty. They are also assigned to the Court System as well. This is the courts ace in the hole. If the FBI won't do the arrest, the US Marshals also have the ability. And sense they work closer to the Court System than they do for the FBI They actually fall under United States Code, Title 28, Chapter 37 of the Judicial Code. That means, they are actually about half assigned to the Court System by tradition and by tradition and custom work for the Court System. Even though their boss is the IG. The Congress can issue a contempt order but will have to get a court to act on it. At that point, even the President can be arrested and charged by the Court if they agree and issue the same order and it's not followed up on. Even though the US Marshals are still under the IG, technically, they are a different law enforcement branch than the other standard DOJ units. And they are also the oldest and have the most tradition. Unlike the FBI and all the others, they were created in 1789 under President Washington. If I were Barr, I wouldn't want to try and block the US Marshals from serving and enforcing those Court Orders since that is one of their main duties. He may find himself in handcuffs in about 10 minutes. Things are going to get very interesting.