Special counsel Robert Mueller has put the Trump White House on notice: preserve all the information relating to Donald Trump Jr.'s Russia meeting.

The letter from Mueller began: "As you are aware the Special Counsel's office is investigating the Russian government's efforts to interfere in the 2016 presidential election, including any links or coordination between the Russian government and individuals associated with the campaign of Donald Trump. Information concerning the June 2016 meeting between Donald J Trump Jr and Natalia Veselnitskaya is relevant to the investigation."

The preservation request is broad and includes text messages, emails, notes, voicemails and other communications and documentation regarding the June 2016 meeting and any related communication since then.

What happens when Trump’s people claim there are no documents, or just go ahead and destroy them despite Mueller’s request? That’s one more constitutional-crisis-style question we may learn the answer to all too soon.