CHICAGO (CBS) — U.S. Sen. Dick Durbin (D-Illinois) has joined another top Democrat on Capitol Hill in suggesting President Donald Trump is helping federal investigators build an obstruction of justice case against himself through the president’s constant use of Twitter to criticize the Russia probe.

After former national security adviser Michael Flynn pleaded guilty last week to lying to the FBI as it investigated Russian interference in the 2016 presidential election, Durbin said the Senate Judiciary Committee is starting to see the assembly of an obstruction case President Trump.

“He tweets constantly. He says things that are damaging to his reputation and to the United States, and he does it at all hours of the day and night. I don’t understand that kind of personality, but clearly he has established a body of evidence, and many of those elements are going to be used against him,” Durbin said.

Speaking on NBC’s “Meet The Press” on Sunday, Sen. Dianne Feinstein (D-California) said a Senate investigation into Russia’s interference in last year’s presidential election has revealed a possible obstruction of justice case against Trump, and the evidence is coming partly from the president himself.

“I see it in the hyper-frenetic attitude of the White House, the comments every day, the continual tweets. And I see it most importantly in what happened with the firing of Director [James] Comey, and it is my belief that that is directly because he did not agree to ‘lift the cloud’ of the Russia investigation. That’s obstruction of justice,” Feinstein said.

Durbin said he has “the highest confidence” in Robert Mueller, the former FBI director who is leading the special prosecutor’s Russia investigation.

“He should be allowed to do his job, and Congress should stand up with one voice – Democrats and Republicans – against anyone at any level of our government that tries to stop it,” he said.

Sen. Lindsey Graham (R-South Carolina) has warned the president to tread cautiously in his comments about the Russia probe and Comey.

“There’s an ongoing criminal investigation; Comey may be part of it. You tweet and comment regarding ongoing criminal investigations at your own peril. I’d be careful if I were you, Mr. President. I’d watch this,” he said Sunday on CBS’s “Face the Nation.’

In a weekend tweetstorm, the president said the FBI’s “reputation is in Tatters – worst in History!” after Comey ran the agency for nearly four years before Trump fired him amid an investigation into the Trump campaign’s ties to Russia and Russia’s interference in the 2016 election.

Graham said he disagrees with Trump’s assessment of the FBI’s reputation, but said Comey needs to answer questions about his time as director.

“I think he made some decisions that, they were really very, very wrong,” Graham said.

In light of Flynn’s guilty plea to lying to the FBI as part of the special counsel’s investigation, Graham said “what Flynn lied about is not a crime.”