“They have arrest power they just don’t use it.”
Indeed they do, but have never used to my knowledge. They would presumably send the sergeant at arms out with Federal marshals to slap the cuffs on.
It was considered with Eric Holder after the full House voted to hold him in Contempt of Congress, but Obummer stepped up and insisted that Holder was covered under executive privilege in some manner so they eagerly stepped back from treading on very delicate new ground.