Sen. Dianne Feinstein on Wednesday asked key current and former advisers to President Trump for an interview with the Senate Judiciary Committee to help its investigation into Russia's meddling in the 2016 election.

Feinstein, the top Democrat on the committee, sent letters to former White House chief of staff Reince Priebus, Trump’s former longtime bodyguard and confidant Keith Schiller, and current White House communications director Hope Hicks on Wednesday asking for interviews and information related to the president’s firing of former FBI Director James Comey and former national security adviser Michael Flynn.

Feinstein also asked the three for documents pertaining to a June 2016 meeting at Trump Tower involving Donald Trump Jr. and a Russian lawyer, which Trump Jr. attended after he was promised damaging information on Hillary Clinton.

The California Democrat asked Schiller for communications related to a trip Trump took to Moscow in 2013 for the Miss Universe Pageant, and requested from Hicks all documents tied to “efforts to obtain or share ‘hacked’ emails” from the Democratic National Committee, John Podesta, and Clinton.

Feinstein wants Priebus, Hicks, and Schiller to appear before the Senate Judiciary Committee for interviews in January.

Neither of the letters is signed by Sen. Chuck Grassley, R-Iowa, the committee’s chairman.

The Senate Judiciary Committee is one of several probing Russia’s interference in the 2016 election and possible collusion between the Trump campaign and Moscow. But Feinstein decided last month to pursue different aspects of the investigation than Grassley.

Since then, she has made inquiries to a number of former Trump campaign advisers. Feinstein is specifically examining whether the president obstructed justice when he fired Comey in May, as well as possible collusion.