He can by command of the House go and assemble the Capitol Police (hardnosed types to a one), take that staff and march into the IRS with a warrant for the arrest of the leader of the IRS and physically take him and all who oppose the lawful action to be dumped before the House and then confined for up to 12 months with no recourse by Trump. As a legitimate power of Congress, the SCOTUS cannot get involved in a lawful act.
The guy with that big stick?
I'm sure some may think he looks pleasant and harmless, much like Doug Marcaida does to the ignorant, but here's his bio.
The Honorable Paul D. Irving was sworn in as the Sergeant at Arms of the U.S. House of Representatives on January 17, 2012, during the 2nd session of the 112th Congress. He is the thirty-sixth person to hold this post since the House of Representatives first met in New York City in 1789. Prior to this, Mr. Irving was an Assistant Director of the U.S. Secret Service from 2001 to 2008, serving as a Special Agent with the Secret Service for 25 years.
No one will fuck with this guy doing his duty and he can walk in and drag people out before someone says "WTF".
Edit- didn't complete my thought.
The House issue an a subpoena to the IRS official who is not complying with a lawful Constitution summons to produce the required information by a drop-dead date. Barr will likely issue an unlawful order to disobey that summons at which point Barr will likely believe that the House won't do a thing, and he's probably right, but not because they can't. They do not have to refer this to the AG to arrest himself and the IRS chief as some think, but there do so on their sole authority. There is a historical precedent and a Constitutional power to arrest and confine for contempt. It is not subject to Executive fits nor Judicial review when used for this purpose.
This is how it could be done. Upon non-compliance, those in the House who so choose can vote for contempt and at that moment send an already assembled team to immediately arrest and haul the IRS chief before the House. The Staff ought to be carried by the Sgt at Arms along with the appropriate arrest order. The Staff shows that the Sgt is performing his lawful duty as authorized by the House and out they go before anyone says "WTF".
Barr can bitch, Trump can rage and they both can go screw off.