Special counsel Robert Mueller is now investigating whether President Donald Trump‘s tweets about Attorney General Jeff Sessions and former FBI Director James Comey amount to obstruction of justice, The New York Times reported Thursday.

Mueller is looking into whether the president intimidated witnesses or sought to end the investigation. The interest is part of of a broader inquiry that includes misleading statements from the White House and the dangling of pardons to possible witnesses. According to the Times, some questions that  Mueller want’s to ask Trump, refer to specific tweets, such as “What was the purpose of your May 12, 2017, tweet?” This specific post came after news of the president’s private dinner with Comey.

The president’s attorney, former New York mayor Rudy Giuliani, dismissed the special counsel’s interest in Trump’s posts. “If you’re going to obstruct justice, you do it quietly and secretly, not in public,” Giuliani told the Times.

It is not clear what Mueller will do if he concludes he has enough evidence to prove that Trump committed a crime. If Mueller does not plan to make a case in court, a report of his findings could be sent to Congress, leaving it to lawmakers to decide whether to begin impeachment proceedings.