How do we know Trump is terrified by Papadopolous plea? His Twitter feed went silent all day
President Donald Trump takes a moment before taking the stage during a Memorial Day ceremony at Arlington National Cemetery in Arlington, Va., May 29, 2017. (DOD photo by U.S. Air Force Tech. Sgt. Brigitte N. Brantley)

Panelists on MSNBC's agreed the bombshell guilty plea revealed Monday in the Trump-Russia probe was bigger news than the indictments of Paul Manafort and Rick Gates.

The best evidence of the plea's importance was that President Donald Trump suddenly had nothing to say after the special counsel announced former foreign policy adviser George Papadopoulos had agreed to plead guilty to lying to FBI agents.

"If you noticed (Monday) there was a tweetstorm that fell silent once the Papadopoulos news came out," said Heidi Przybyla, senior political correspondent of USA Today. "Now we are getting hotter on the question of collusion, now you have a second campaign official who potentially colluded with the Russians. The Russians were aggressive, they were shopping these emails, they had a receptive potential buyer here in these high-level aides."

The court documents showed Papadopoulos had been a cooperating witness since his July 27 arrest, and Przybyla said those words "should chill the Trump campaign and officials."

"He pled to a less serious charge, that is classic case of him cooperating," Przybyla said. "This railing about leaks, this is being held quite quiet. This is only the beginning of charges either for Manafort and for additional people, and we simply don't know where the top of the fish head is."

MSNBC's Mike Barnicle said the revelations in those court documents, signed by Papadopoulos, described a nearly textbook definition of collusion.

"If you read the indictment, and collusion is defined as a secret agreement or cooperation especially for an illegal or deceitful purpose, that revelation (Monday) is the definition of collusion," Barnicle said. "So now have you the introduction of the reality of collusion into the White House."