The 53-year-old is accused of lying about his drug use in October 2018 on a form to buy a gun, which he kept for around 11 days.

While the president's son has admitted to struggles with a crack cocaine addiction over the period in question, his lawyers insist he didn't break the law.

Abbe Lowell, his lawyer, told the court in Wilmington, Delaware, on Tuesday he plans to file a motion to dismiss the case, challenging their constitutionality.

These kind of gun charges are rare, and an appeals court has found banning drug users from guns violates the Second Amendment.

In a potential headache for President Biden, the case remains on track for a possible trial just as the 2024 election looms.

It comes after a plea deal fell apart at a court hearing in July, which revolved around tax and gun charges, after the District Judge Maryellen Noreika raised a series of questions about the deal.

Federal prosecutors had been looking into his business dealings for five years - but the agreement would have avoided criminal proceedings before his father was actively campaigning for president in 2024.

Mr Biden's legal team is suggesting prosecutors bowed to pressure by Republicans - who have argued the Democratic president's son got a sweetheart deal - and that the charges were the result of political pressure.

Now, however, a special counsel has been appointed to handle the case and while no new tax charges have been filed, they could come in Washington or in California, where Hunter Biden lives.

On the gun charges, two counts are tied to the president's son allegedly filing a form claiming he was not using illegal drugs at the time he purchased a revolver in October 2018.

The third alleges he possessed a firearm while using a narcotic.

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

Republicans have accused Mr Biden, who has worked as an investment banker, lobbyist, lawyer and artist, of wrongdoing relating to Ukraine and China.

They have also made him a focus of a congressional impeachment inquiry of Joe Biden.

Hunter Biden, who has publicly discussed his drug abuse, has 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.

The case remains on track for a possible trial just as the 2024 election looms.