Former senator reveals to Maddow how one brave Democrat can reveal key document in impeachment trial

Near the end of Wednesday's impeachment trial, Chief Justice John Roberts announced that an agreement had been made to allow senators to read supplemental testimony from Vice President Mike Pence aide Jennifer Williams.

The document will remain classified, despite claims that there is no classified material in the document, only evidence that is damning to the president.

"In terms of this document potentially being improperly classified, which is something that has been raised in writing by Rep. Adam Schiff (D-CA) and raised on the floor of the Senate tonight by Rep. Zoe Lofgren (D-CA)," MSNBC anchor Rachel Maddow noted. "Obviously, it was the vice president's office that said it was classified, they are getting publicly criticized for that. If it has been improperly classified and it should be something that the public can see, who adjudicates that?"

"Well, it's complicated. Ultimately a court does if it gets to that," said former Sen. Claire McCaskill (D-MO). "You can't classify things just to keep them out of the public eye, there has to be a rational basis for the classification. And ultimately it would be a matter for the judges."

The former lawmaker noted another dynamic.

A single Democratic senator could make the decision to read the document into the record or summarize it, on the Senate floor.

In theory, the senator would be protected from prosecution by the constitution's speech and debate clause.

As McCaskill noted, the decision flips the burden of proof, making the administration prove that the document should have been classified.

Following today's impeachment trial, all 47 Senate Democrats were allowed to view the document in a secure room. Under McCaskill's theory, it would only take bravery from a single member to reveal if the Trump administration and Pence are unproperly classifying documents to cover-up wrongdoing.

Watch: