OPINION: Why Hope Hicks and Don McGahn testimony is key

(How many times can the White House slap Congress in the mouth before Congress hits back? The list got longer this week when the White House instructed former Trump administration officials Hope Hicks and Annie Donaldson to defy a House Judiciary Committee subpoena for documents relating to their work in the White House. Hicks and Donaldson now join other subpoena recipients -- Attorney General William Barr, former White House counsel Don McGahn, Treasury Secretary Steve Mnuchin -- in telling Congress to pound sand.

The White House's latest act of defiance drove home a message that already should have been clear to Congress: you'll get nothing and that's that. Now Congress needs to end its equivocating and take decisive action to enforce its subpoena power. The only way to do this is to play hardball: promptly hold all who defy subpoenas in contempt, bring every contested subpoena to court to seek enforcement and demand expedited rulings to prevent the White House from prevailing by running out the clock. This isn't about machismo or ego -- this is about constitutional balance of powers.

The House Judiciary Committee will hold hearings next week designed to bring to life the findings of special counsel Robert Mueller's report. Former Richard Nixon White House counsel John Dean (a current CNN contributor) and a panel of former federal prosecutors and legal experts will reportedly discuss the evidence set forth in the report.

The hearings will be important because so many Americans -- including some members of Congress -- have not read the full Mueller report. Any trial lawyer understands that written reports only resonate so much, but live testimony tends to make a bigger impact. It will be a worthwhile exercise for experienced witnesses to explain Mueller's findings to Congress and the public.

But, standing alone, these hearings will be insufficient if Congress' goal is to ensure accountability from President Donald Trump and the White House. The most meaningful testimony would come not from outside experts but rather from McGahn, Hicks and others who witnessed Trump's potentially obstructive acts firsthand and thus far have been directed by the White House to brush off congressional subpoenas.