The ranking Democrat of the Senate judiciary committee and its Republican chairman have reached a deal to subpoena former Trump campaign chairman Paul Manafort in order to make him attend a public hearing.

Sen. Dianne Feinstein (D-Calif.) told CNN Wednesday the she and Chairman Chuck Grassley (R-Iowa) have agreed to terms regarding Manafort as part of the committee’s investigation into Russia’s alleged interference in the 2016 presidential election and possibly the FBI during both the Trump and Obama administrations.

A Feinstein spokesperson told CNN that the subpoena agreement is “in principle” and that details are still being hammered out. Grassley also confirmed the deal to the outlet and said that specific details are being finalized.

Manafort’s office did not immediately respond to TIME’s request for comment.

Manafort has tried to avoid appearing at a public hearing on the matter in recent months, cutting a deal with investigators in July in exchange for documents and a closed-door, transcribed interview with the committee. President Donald Trump’s son, Donald Trump Jr., took the same deal.

But Grassley has apparently grown frustrated with Manafort since then, according to CNN, because his lawyers have not cooperated with the committee’s request.

If successfully arranged, the hearing will almost certainly discuss a June 2016 meeting in which Manafort, Trump Jr. and senior adviser to the President and son-in-law Jared Kushner spoke with Russians who claimed to have incriminating information about Hillary Clinton’s campaign.

Manafort has also been under the scrutiny of Special Counsel Robert Mueller, who as part of his own Russia probe last month had FBI agents raid Manafort’s home in the middle of the night with him and his wife sleeping inside.

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