Special counsel Robert Mueller is looking to US President Donald Trump’s Twitter account for potential evidence of obstruction of his investigation.

According to three anonymous sources on Thursday, Special counsel Robert Mueller is investigating whether U.S. President Donald Trump’s tweets constitute an attempt to obstruct justice with respect to the probe into his campaign’s ties with Russia, The New York Times reported Thursday.

Citing three unnamed people briefed on the subject, the sources said that Mueller, a former FBI director, was scrutinizing tweets and negative statements from the president about Attorney General Jeff Sessions and Mueller’s FBI successor, James Comey.

Trump has repeatedly turned to Twitter to try to bend proceedings and public opinion in the direction he would like — calling for Mueller’s probe to end and demanding that the Justice Department investigate his political enemies.

In one of many similar tweets, Trump on April 20 appeared to try to undermine Mueller’s probe into whether the Trump campaign colluded with Russia in its efforts to skew the 2016 US presidential election.

A Republican-controlled Senate panel has said recently that further evidence has been found to support a US intelligence assessment that Russia interfered in the 2016 presidential election to help elect Donald Trump.

Meanwhile, a group of Republican lawmakers on Wednesday introduced articles of impeachment to remove deputy U.S. Attorney General, Rod Rosenstein, escalating a fight over Special Counsel Robert Mueller’s investigation of alleged Russian meddling in the 2016 U.S. presidential election.

A special counsel, Robert Mueller,  is investigating possible collusion between Russia and members of Trump’s campaign team. Three campaign aides have pleaded guilty to lying to the FBI and Trump’s former campaign chief, Paul Manafort, is in jail awaiting trial on charges of financial crimes.