United States Attorney General Jeff Sessions was questioned in the case of the alleged Russian meddling in the 2016 presidential elections on Tuesday, Reuters reported. He was interrogated by Robert Mueller, a former director of the US Federal Bureau of Investigation.

This is the first time Mueller interviewed a member of President Donald Trump’s Cabinet. He now wants to question Trump on the case, a report in The Washington Post said.

Mueller is believed to have told Trump’s lawyers he will question the president about why he fired former FBI Director James Comey and former National Security Adviser Michael Flynn, The New York Times quoted a source who was briefed about the matter.

Mueller has already interviewed several of Trump’s aides and family members. His focus on why Flynn and Comey were sacked shows that his team is looking into possible obstruction of justice, The Guardian.

The White House said it will cooperate with Mueller’s investigation.

Sessions was a key adviser for the Trump campaign in the run-up to the 2016 presidential elections, which intelligence sources say were manipulated by Russia. In March 2017, Sessions had recused himself from the investigations into the inquiry after reports on his undisclosed meetings with Russian officials surfaced.