Chairman Chuck Grassley said the panel would subpoena Donald Trump Jr. and Paul Manafort if they refused to appear.

| J. Scott Applewhite/AP Grassley threatens to subpoena Trump Jr., Manafort

The top Republican on the Senate Judiciary Committee said Thursday that the committee would subpoena President Donald Trump’s eldest son — Donald Trump Jr. — if he refuses to voluntarily testify next week at a hearing on Russian interference in the 2016 presidential election.

Chairman Chuck Grassley (R-Iowa) also said the panel would subpoena Paul Manafort, who was Trump’s campaign chairman for part of 2016, if he refuses to appear.

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"That’s all taken care of in our letter and statements I've made,” Grassley said. “If they don’t voluntarily come, they’ll be subpoenaed."

Grassley's committee on Wednesday issued an extensive list of document requests to both men, as well as to the Trump Organization and campaign.

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Manafort and Trump Jr. have yet to indicate whether they plan to appear next week, for a panel that’s part of a broader hearing on foreign influence in elections.

Trump Jr. has publicly indicated that he’s willing to cooperate with congressional investigators.

Jared Kushner, Trump’s son-in-law and a top adviser, is planning to testify next week in a closed session of the Senate Intelligence Committee.