[Ray76]

The House and Senate each have their Sgt at Arms who have the authority to arrest persons defying Congressional subpoenas. They can and have done so.

To say that Congress must rely on another Branch for enforcement is absurd.

[Mariner]

"To say that Congress must rely on another Branch for enforcement is absurd."

Do you know of cases where the Sgt at Arms has traveled outside DC to arrest somebody for contempt or failure to appear?

I know of none.

Congress relies on the DOJ for those services.

[Mariner]

One other note: The House has arrested two Executive Branch officials...via the Sargent at Arms...twice in the history of the US. Both times in DC. (WikiPedia)

What are they going to do, send the Capitol Police to Maryland...or Ohio to serve the warrant?

That's what's absurd.