Rudy Giuliani, President Donald Trump’s personal lawyer, is being investigated by federal prosecutors for possible campaign finance violations and a failure to register as a foreign agent as part of an active investigation into his financial dealings, according to three U.S. officials.

The probe of Giuliani, which one official said could also include possible charges on violating laws against bribing foreign officials or conspiracy, presents a serious threat to Trump’s presidency from a man that former national security adviser John Bolton has called a “hand grenade.”

A second official said Giuliani’s activities raise counterintelligence concerns as well, although there probably wouldn’t be a criminal charge related to that. The officials, who asked for anonymity to discuss a sensitive matter, provided the first indication of the potential charges under investigation.

Giuliani is a central figure in the U.S. House impeachment inquiry, which focuses on an effort led by the former New York City mayor to pressure Ukraine’s government to investigate the president’s political rivals. If Giuliani is charged or indicted, he could expose Trump to a new level of legal and political jeopardy, especially if he’s accused of committing a crime on the president’s behalf.

“I would not be surprised if he gets indicted,” said Mimi Rocah, a former federal prosecutor with the U.S. Attorney’s Office for the Southern District of New York. “It’s clear Giuliani is up to his ears in shady stuff and there’s tons of smoke.”

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