Democratic Rep. Ted Lieu (Calif.) warned on Saturday that special counsel Robert MuellerRobert Swan MuellerSasse: US should applaud choice of Mueller to lead Russia probe MORE "knows far more than people think," pointing to a new report on the Trump campaign's alleged dealings with Russia.

Lieu pointed to a Saturday New York Times report that found former Trump campaign foreign policy adviser George PapadopoulosGeorge Demetrios PapadopoulosFlynn sentencing move spurs questions about duration of Mueller probe Time for sunshine on Trump-Russia investigation Trump to declassify controversial text messages, documents related to Russia probe MORE inadvertently triggered the FBI's investigation into Russian collusion by reportedly drunkenly telling to an Australian diplomat details of Russians possessing Democratic Party emails.

"Important story below," Lieu tweeted. "Keep in mind no one was really aware of George Papadopoulos until his guilty plea was revealed. That tells us Special Counsel Mueller knows far more than people think. And Papadopoulos is cooperating with Mueller. The White House should be scared."

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Papadopoulos pleaded guilty to lying to the FBI about his conversations with Russians during the election, which were aimed at setting up a meeting between President TrumpDonald John TrumpSunday shows preview: Trump sells U.N. reorganizing and Kavanaugh allegations dominate Ex-Trump staffer out at CNN amid “false and defamatory accusations” Democrats opposed to Pelosi lack challenger to topple her MORE and Russian President Vladimir Putin. 

The former aide is now reportedly cooperating with Mueller, who has indicted three other former Trump campaign associates in his investigation, which he and his team of federal prosecutors took over from the FBI. 

The California lawmaker is a member of the House Judiciary Committee, which has interviewed former Trump campaign team members about their knowledge of communications with Russia.

Lieu has fiercely defended Mueller's team despite criticism from Republicans, and has warned Trump of the political fallout that could result from firing the top investigator.