WASHINGTON — Attorney General William Barr has agreed to testify before the House Judiciary Committee next month, appearing for the first time before the panel as questions swirl about whether he intervened in the case of a longtime ally of President Donald Trump.

House Judiciary Committee Chairman Jerrold Nadler, D-N.Y., released a letter Wednesday to Barr “to confirm your agreement to testify” on March 31. In the letter, Nadler and committee Democrats write that they have concerns that Barr has misused the criminal justice system for political purposes.

“In your tenure as attorney general, you have engaged in a pattern of conduct in legal matters relating to the president that raises significant concerns for this committee,” Nadler and the Democrats wrote.

The Justice Department confirmed Barr would testify. His appearance will be the first before the House Judiciary panel since he became attorney general a year ago, and since he declined an invitation to testify about special counsel Robert Mueller’s report after it was released.

The Democrats said they plan to ask Barr about the department’s decision this week to overrule four federal prosecutors and lower the amount of prison time it would seek for Trump’s confidant Roger Stone. The four prosecutors immediately quit the case, in which Stone was convicted of lying to Congress, witness tampering and obstructing the House investigation into whether the Trump campaign coordinated with Russia to tip the 2016 election.

Trump tweeted congratulations to Barr “for taking charge of a case that was totally out of control and perhaps should not have been brought,” suggesting the prosecutors had gone rogue.

The department insisted the decision to undo the sentencing recommendation was made Monday night, before Trump began tweeting about it, and that prosecutors had not spoken to the White House about it.