NEW YORK (AP) — With Merrick Garland poised to be confirmed as attorney general as early as next week, one of the first major questions he is likely to encounter is what to do about Rudy Giuliani.

A federal probe into the overseas and business dealings of the former New York City mayor and close ally of former President Donald Trump stalled last year over a dispute over investigative tactics as Trump unsuccessfully sought reelection and amid Giuliani’s prominent role in subsequently disputing the results of the contest on Trump’s behalf.

But the U.S. attorney's office in Manhattan has since returned to the question of bringing a criminal case against Giuliani, focusing at least in part on whether he broke U.S. lobbying laws by failing to register as a foreign agent related to his work, according to one current and one former law enforcement official familiar with the inquiry. The officials weren't authorized to discuss the ongoing case and spoke on the condition of anonymity.

The arrival of a new leadership team in Washington is likely to guarantee a fresh look at the investigation. No matter how it unfolds, the probe ensures that a Justice Department looking to move forward after a tumultuous four years will nonetheless have to confront unresolved, and politically charged, questions from the Trump era — not to mention calls from some Democrats to investigate Trump himself.

The full scope of the investigation is unclear, but it at least partly involves Giuliani's Ukraine dealings, the officials said.

Giuliani was central to the then-president's efforts to dig up dirt against Democratic rival Joe Biden and to press Ukraine for an investigation into Biden and his son, Hunter — who himself now faces a criminal tax probe by the Justice Department. Giuliani also sought to undermine former U.S. ambassador to Ukraine Marie Yovanovitch, who was pushed out on Trump's orders, and met several times with a Ukrainian lawmaker who released edited recordings of Biden in an effort to smear him before the election.

The Foreign Agents Registration Act requires people who lobby on behalf of a foreign government or entity to register with the Justice Department. The once-obscure law, aimed at improving transparency, has received a burst of attention in recent years, particularly during an investigation by former special counsel Robert Mueller that revealed an array of foreign influence operations in the U.S.

Federal prosecutors in Manhattan pushed last year for a search warrant for records, including some of Giuliani's communications, but officials in the Trump-era Justice Department would not sign off on the request, according to multiple people familiar with the investigation who insisted on anonymity to speak about an ongoing investigation.

Officials in the deputy attorney general's office raised concerns about both the scope of the request, which they thought would contain communications that could be covered by legal privilege between Giuliani and Trump, and the method of obtaining the records, three of the people said.

The Justice Department requires that applications for search warrants served on lawyers be approved by senior department officials.

“They decided it was prudent to put it off until the dust settled, and the dust has settled now,” said Kenneth F. McCallion, a former federal prosecutor who represents Ukrainian clients relevant to the inquiry and has been in contact with federal authorities about the investigation.

McCallion declined to identify his clients, saying he had not been authorized to do so. He previously has represented former Prime Minister Yulia Tymoshenko.

Giuliani's attorney Robert J. Costello told The Associated Press he has “heard nothing” from federal prosecutors concerning Giuliani.

It is possible that Giuliani could try to argue that his actions were taken at the behest of the president rather than a foreign country, and therefore registration would not be required under federal law.

Giuliani wrote in a text message Thursday to the AP that he “never represented a foreign anything before the U.S. government.”

"It’s pure political persecution,” he said of the investigation. The U.S. attorney’s office declined to comment.

McCallion said federal authorities were asking questions concerning a wide range of Giuliani’s international business dealings, and that “everything was on the table” as it pertained to his work in Ukraine. He said the inquiry was not entirely focused on Ukraine, but declined to elaborate.

The investigation of Giuliani's lobbying first came to light in October 2019, when The New York Times reported that federal prosecutors were investigating Giuliani's efforts to oust Yovanovitch, who was recalled amid Trump’s bid to solicit dirt from Ukraine to pressure Ukraine into helping his reelection prospects.

Federal prosecutors also have investigated Giuliani as part of a criminal case brought against his former associates, Lev Parnas and Igor Fruman, Soviet-born business partners from Florida who played key roles in Giuliani’s efforts to launch the Ukrainian corruption investigation against the Bidens.

Parnas and Fruman were charged in a scheme to make illegal campaign donations to local and federal politicians in New York, Nevada and other states to try to win support for a new recreational marijuana business.

Giuliani has said he had no knowledge of illegal donations and hadn’t seen any evidence that Parnas and Fruman did anything wrong.

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Tucker and Balsamo reported from Washington. Associated Press writer Larry Neumeister contributed to this report from New York.