WILMINGTON, Delaware President Joe Biden's son Hunter Biden is expected to plead not guilty on Tuesday to lying about his drug use while buying a handgun, in the first-ever criminal prosecution of a sitting U.S. president's child.

Hunter Biden, 53, was charged last month by U.S. Special Counsel David Weiss with three counts related to lying on a federal form to acquire a Colt Cobra handgun in 2018 and for being an illegal drug user in possession of the gun.

His lawyer, Abbe Lowell, said in a court filing last month that Hunter Biden plans to plead not guilty.

That sets the stage for a historic first: The criminal trial of the adult child of a sitting president who is campaigning for reelection.

Biden's likely 2024 Republican rival, Donald Trump, faces four upcoming criminal trials of his own, two of which are tied to his attempts to overturn his 2020 election loss to Biden, which he continues to falsely claim is the result of fraud.

In July, an agreement to resolve the gun charges and separate tax charges unraveled when a U.S. District Judge Maryellen Noreika in Wilmington refused to accept it.

Under that deal, Hunter Biden had agreed to plead guilty to misdemeanor tax violations and would avoid punishment on the gun charges if for two years he did not possess a firearm and refrained from using illegal drugs and alcohol.

Hunter Biden's lawyers have said in court filings they believe the agreement with prosecutors remains in effect and that Hunter Biden continues to comply with it. They accused prosecutors of reneging on the agreement.

Some legal experts have said that any firearms-related charges against Biden could be vulnerable to a constitutional challenge, after the U.S. Supreme Court last year in a landmark ruling expanded gun rights under the U.S. Constitution's Second Amendment, which protects the right to bear arms.

The younger Biden for years has been the focus of unrelenting attacks by Republicans, led by former President Trump.

Republicans have accused Hunter Biden, who has worked as a lobbyist, lawyer, investment banker and artist, of wrongdoing relating to Ukraine and China and have made him a focus of a congressional impeachment inquiry of Joe Biden.

The president's son, who has publicly discussed his substance abuse, never held a position in the White House or on his father's campaign. The president has said he has not discussed foreign business dealings with his son and has said his Justice Department would have independence in any investigation of a member of his family.

(Reporting by Tom Hals in Wilmington, Delaware; Editing by Scott Malone and Alistair Bell)