WASHINGTON (AP) — In offering Ukraine's president the help of Attorney General William Barr in investigating rival Joe Biden, President Donald Trump is once again inserting the nation's top law enforcement officer in a political fray.

It's a role Barr has embraced since taking command of the Justice Department in February, most notably by casting special counsel Robert Mueller's report on the Russia investigation as a vindication for Trump, even though Mueller pointedly said he was not exonerating Trump of obstructing justice.

But even as one of the Republican president's greatest defenders, Barr has sought to distance himself from Trump's conversations with Ukrainian President Volodymyr Zelenskiy. The Justice Department insists he was unaware the president had said he would help investigate a political rival.

Attorneys general traditionally strike a delicate political balance. As members of the Cabinet, they are expected to back a president's law enforcement agenda. Barr has done that — emphasizing some of the president's main talking points and standing shoulder-to-shoulder with Trump in defending key policy decisions. But as the heads of the Justice Department, attorneys general are expected to be above politics and not let political considerations guide their actions.

Trump inserted Barr into the latest political firestorm, one that has led to a House impeachment inquiry, when he asked Zelenskiy to dig up dirt on Democratic presidential candidate Biden, and indicated Barr and Trump confidant Rudy Giuliani would be in touch.

"There's a lot of talk about Biden's son, that Biden stopped the prosecution and a lot of people want to find out about that so whatever you can do with the Attorney General would be great," Trump said in the July 25 conversation , according to a rough transcript the White House released on Wednesday. There is no evidence that Biden's son was ever under investigation in Ukraine.

In the call, Trump seemingly equates Barr with Giuliani, who has no role in the administration and, in rambling television appearances, is one of Trump's most vocal defenders.

Rep. Jerrold Nadler, D-N.Y., chairman of the House Judiciary Committee, said Wednesday that Barr must step aside from the Ukraine investigation now that the transcript shows that Trump "dragged the Attorney General into this mess."

Barr saw no need to recuse himself after the Justice Department was made aware of a whistleblower's complaint about the conversation and other matters. The intelligence community's internal watchdog had raised concerns that in the call Trump may have violated campaign finance law.

The Justice Department found no crime, and the matter is now closed. Those close to the attorney general argue there would have been no reason for him to recuse, or even consult ethics officials, because he was unaware of the president's conversation at the time it occurred and was not involved in any discussion of investigating Biden and his son Hunter.

In a statement, the Justice Department sought to distance Barr from the situation, insisting that the attorney general was unaware the president offered him up to investigate one of the president's political rivals.

"The President has not spoken with the Attorney General about having Ukraine investigate anything relating to former Vice President Biden or his son. The President has not asked the Attorney General to contact Ukraine - on this or any other matter. The Attorney General has not communicated with Ukraine - on this or any other subject. Nor has the Attorney General discussed this matter, or anything relating to Ukraine, with Rudy Giuliani," Justice Department spokeswoman Kerri Kupec said in the statement.

The attorney general was generally aware of the whistleblower complaint after it was submitted to the Justice Department, weeks after the call, a person familiar with the matter said. But Barr was not involved in any of the legal analysis and did not make the decision that the president's actions did not amount to a crime.

The decision was made by Assistant Attorney General Brian Benczkowski, who runs the department's criminal division, in consultation with Deputy Attorney General Jeffrey Rosen, the person said. Both are Trump appointees and Benczkowski also worked on Trump's transition team. Barr and Benczkowski also worked at the same Washington law firm before joining the administration.

The person spoke to The Associated Press on condition of anonymity in order to discuss internal investigative deliberations.

Trump has repeatedly lauded Barr, a stark contrast from his relationship with his first attorney general, Jeff Sessions. He believed Sessions needlessly stepped aside from the Russia investigation, a decision that Trump blamed for the eventual appointment of Mueller.

By contrast, Barr uncomplainingly carries out the president's agenda. Not only did Barr provide the first, favorable framing for the Mueller report, but he also appointed a U.S. attorney to investigate the origins of the probe. That investigation, which Barr is overseeing himself, is looking into whether there was wrongdoing committed by those who launched the investigation into whether the Trump campaign coordinated with Russia ahead of the 2016 presidential election.

Under Barr, the Justice Department has supported the White House's decision to claim broad executive privilege to prevent the testimony of administration officials that could be potentially damaging for Trump. Barr has also defied subpoenas from Congress — in line with the Trump administration's stance to block Democrats' efforts to investigate Trump.

Justice Department lawyers also are deciding whether to join Trump's personal lawyers to fight a New York grand jury subpoena seeking Trump's tax returns.

Barr also has not been reluctant to joust with congressional Democrats.

After a House panel voted to hold him in contempt, Barr baited House Speaker Nancy Pelosi at an event on Capitol Hill in May, asking her if she brought her handcuffs to arrest him.

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Associated Press writer Juana Summers contributed to this report.