WASHINGTON (AP) — House Democrats frustrated over the Senate's acquittal of President Donald Trump are pushing their oversight efforts toward the Justice Department and what they call Attorney General William Barr's efforts to politicize federal law enforcement.

Democrats have demanded more information about Barr's intervention in the case of Roger Stone, a longtime Trump confidant who was convicted in November of lying to Congress and other charges. Barr this week overruled prosecutors who had recommended that Stone be sentenced to 7 to 9 years in prison.

House Speaker Nancy Pelosi criticized Barr on Thursday, calling him one of Trump's "henchmen."

"The attorney general has stooped to such levels," Pelosi said. "What a sad disappointment. The American people deserve better."

The sharpened look at Barr's activities comes at a time when many Democrats appear wary of prolonging the Ukraine inquiry that led to Trump's impeachment. Pelosi and House Intelligence Committee Chairman Adam Schiff have put off — but not ruled out — a subpoena for former National Security Adviser John Bolton, who refused to participate in the House impeachment inquiry but later said he would testify in the Senate trial. Bolton is writing a book.

Issuing a subpoena for Bolton could bring dramatic testimony about Trump's conduct, but also risk a court fight that could take months to resolve. Many Democrats privately say they want to look forward, not backward, and conduct oversight of the Republican president's actions in real time.

First up will be examining whether Barr inappropriately intervened in the Stone case. 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 congratulated the attorney general afterward on Twitter. Meanwhile, the four prosecutors on the case immediately withdrew.

The turmoil within the Justice Department has given Democrats a new way forward for their investigations after the sting of the Senate's impeachment acquittal. While there is little interest in pursuing another impeachment case, Democrats want to leverage the power of their majority to conduct oversight as they try to defeat Trump at the polls in November.

"The resignation and defection of these prosecutors is a huge alarm bell going off in our system," said Rep. Jamie Raskin of Maryland, one of the most vocal Democrats on the House Judiciary Committee who pushed for impeachment. "So, that is the immediate emergency."

House Judiciary Committee Chairman Jerrold Nadler announced Wednesday that Barr will testify before the committee March 31 and that lawmakers will ask him about his involvement in the Stone case. People familiar with the committee's plans said there could be other Judiciary committee hearings before then that examine the politicization of the department. The people requested anonymity because the plans aren't yet set.

Barr appeared to try and deflect some of the rising criticism Thursday, saying in an interview with ABC News that Trump's tweets about Justice Department prosecutors and cases "make it impossible for me to do my job." But he also said the decision to undo the sentencing recommendation was made before Trump tweeted about it, and he said the president had not asked him to intervene in any cases.

That answer won't be enough for Democrats, who also want to ask Barr about his decision to take information from Trump's personal lawyer, Rudy Giuliani, about Joe Biden and his son. Those same efforts by Giuliani in Ukraine were at the heart of Trump's impeachment.

"In the past week alone, you have taken steps that raise grave questions about your leadership," the Democrats wrote in a letter to Barr.

The GOP-led Senate has shown less interest in grilling the attorney general. Republicans defended the department's decision to reduce Stone's sentence and said they didn't expect to request Barr's testimony.

"President Trump, in selecting Bill Barr to be attorney general, has done a great service to the people serving in the Department of Justice and our nation as a whole," Senate Judiciary Committee Chairman Lindsey Graham, R-S.C., said in a statement Thursday.

Graham added that Barr has his "complete confidence."

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Associated Press writer Lisa Mascaro contributed to this report.