Good. Last I checked, impeachment trial occurs in the Senate. If they want WH to engage, they can vote on articles of impeachment and send it to the Senate. Until then, it's just a show and POTUS is better off letting them roll around in the mud.
Not sure if someone already posted it, but here's the letter the WH sent in response to Nadler's impeachment hearing.
https://www.scribd.com/document/437787363/White-House-Response-to-HJC-Impeachment-Groundwork-Hearing