Hunter Biden pleaded not guilty Tuesday to charges relating to concealing drug use when buying a weapon, kicking off a battle to beat an indictment from the Justice Department as House Republicans zero in on an impeachment of his father, seeking to tie both Bidens to wrongdoing.

Biden’s court appearance in Delaware, after a judge denied his request to appear by video conference, comes after an initial plea deal in the matter fell apart.

Special counsel David Weiss, also the U.S. attorney for Delaware, charged Biden with failing to disclose drug use when seeking to buy a weapon — resulting in two charges — as well as for unlawful possession of a firearm while addicted to a controlled substance. Biden has spoken openly about his struggles with addiction.

The most serious charges carry up to 10 years in prison and up to $250,000 in fines.

It’s a sharp turnaround from a scrapped plea deal that would have had Biden entering a diversion program on the matter, and prosecutors continue to mull whether to file charges on the tax crimes also initially covered by the deal.

Biden’s attorney, Abbe Lowell, said during the arraignment that he planned to file a motion to dismiss the charges, challenging the constitutionality of a law that blocks drug users from owning guns. It’s a provision he says violates the Second Amendment.

He said he will also move to dismiss the charges, arguing that the initial plea deal would have provided immunity on them.

The criminal case gets underway as GOP lawmakers accelerate their probe into President Biden, having held their first hearing into an impeachment inquiry last week.

The effort got off to a rocky start, with several GOP-invited witnesses saying there was not presently enough evidence to impeach the president, as they could not connect any of his actions to his son’s business dealings, despite claims of influence peddling.

One of the GOP’s main focuses is Weiss’s investigation, amid claims from two whistleblowers that the probe into Hunter Biden was slow-walked.

Weiss has signaled that he may still bring tax charges in other districts, including California and Washington, D.C. — the same locations where the two whistleblowers said they found stronger evidence of tax crimes.

Biden’s arraignment comes the same day that Matthew Graves, the U.S. attorney for D.C., is slated to do a transcribed interview with the House Judiciary Committee, one of the three panels involved in the probe into the Biden family.

Whistleblowers alleged Graves resisted partnering to bring charges against Biden in Washington. 

The Associated Press contributed.

Updated at 1:20 p.m. ET