So what can or should Judge Sullivan do in light of DOJ refusal to turn over documents?

[StarfishSaver]

3. He can find them in contempt of court and order fine or arrest. But arrest will be tricky

since the U.S. Marshals usually carry out enforcement, but the Marshals are actually part of DOJ, meaning the AG oversees them and he's not likely to allow the Marshals to arrest him or any of his attorneys.

It's likely that the Marshals will carry out the judge's order anyway since obeying the AG would mean they are defying a court order themselves. If they refuse, the judge can hold them in contempt, as well.

If the Marshals don't follow the judge's order, the judge could deputize someone outside of the executive branch to conduct the arrests.

But I have a feeling that the judge could find plenty of Marshals somewhere in the country who would be happy to make this arrest ...

I have no idea how this will play out. But it's a mess, isn't it?