The top Democrat on the Senate Judiciary Committee is requesting additional documents from former Trump campaign officials as part of the committee’s investigation into Russian meddling in the 2016 election.

Sen. Dianne Feinstein, D-Calif., the committee’s ranking member, sent letters to former Trump campaign officials Carter Page, Sam Clovis, Walid Phares, and J.D. Gordon on Tuesday requesting information on contacts between Russian officials and members of the Trump campaign.

Feinstein asked Page for documents related to trips he took to Russia in July 2016 and Dec. 2016, as well as communications with Russian officials and Trump campaign advisers, and documents related to the Republican National Committee’s platform regarding Ukraine and Russia.

In her letter to Clovis, the former national co-chairman and chief policy adviser of the Trump campaign, Feinstein requested communications Clovis may have had with Russian officials, and documents related to efforts to obtain or share emails hacked from the Democratic National Committee and John Podesta, Hillary Clinton’s campaign chairman.

Feinstein made similar requests to both Gordon and Phares, who worked on the Trump campaign’s foreign policy team.

The California Democrat also asked Clovis, Phares, and Gordon to appear before the committee for interviews next month.

A number of congressional committees are investigating Russian meddling in the 2016 election and possible collusion between the Trump campaign and Moscow, including the Senate Judiciary Committee.

But Feinstein and Sen. Chuck Grassley, R-Iowa, the committee chairman, decided last month to pursue different paths related to the panel’s Russia probe.

The California Democrat said she planned to examine Trump’s firing of former FBI Director James Comey and whether the president obstructed justice, as well as possible collusion.

As part of her probe, Feinstein has also requested information from the White House, social media companies, and entities associated with the Trump campaign about the campaign’s ties to Russia and Russia’s use of social media platforms during the 2016 election.

Feinstein said additional requests are to be expected.