Former White House counsel Don McGahn must comply with a congressional subpoena seeking his testimony about President Donald Trump's efforts to impede the now-completed federal investigation into Russian interference in the 2016 U.S. election, a judge ruled on Monday.

In an important case about presidential powers, U.S. District Judge Ketanji Brown Jackson in Washington rejected the Trump administration's legal claim that current and former senior White House officials cannot be compelled to testify before Congress.

McGahn, who left his post in October 2018, last May defied a subpoena from the Democratic-led House of Representatives Judiciary Committee for testimony. The subpoena was issued months before the House opened an impeachment inquiry in September into the Republican president's actions concerning Ukraine. The committee sued McGahn in August to try to enforce the subpoena.