Những tội danh về súng đối với Hunter Biden là khá đặc biệt. Đây là lý do tại sao.

On the face of it, Hunter Biden appears at risk of being sentenced to as long as 25 years in prison and $750,000 in fines if he is convicted on the three gun charges brought against him by federal prosecutors on Thursday.

In reality, few people fitting Mr. Biden’s profile — a first-time, nonviolent offender accused of lying on a federal firearms application, who never used the gun (in his case, a Colt Cobra .38 that he held onto for less than two weeks five years ago) to commit a crime — get serious prison time for the offenses charged in the indictment.

Just bringing the charges is out of the ordinary in some ways, former law enforcement officials say, and the legal basis of the prosecution is under constitutional challenge.

Here’s a rundown of the accusations against President Biden’s son and what makes the case unusual.

What are the charges?

The indictment returned by a federal grand jury in Wilmington, Del., charged Mr. Biden with three felonies: lying to a federally licensed gun dealer, which carries a maximum penalty of 10 years in jail; making a false claim on the federal firearms application used to screen applicants, with a sentence of up to five years; and possession of an illegally obtained gun from Oct. 12 to Oct. 23, 2018, which carries a maximum of 10 years.

The charges stem from the purchase of a handgun by Mr. Biden at one of the low points of his troubled life. He had been addicted to crack cocaine, bouncing in and out of rehab, was divorced, using prostitutes and having money problems. The New York Times reported this year that Mr. Biden later recounted to friends going into the gun store on a whim and buying the .38 because he thought spending time at a shooting range would help him avoid using drugs.

In purchasing the gun, Mr. Biden had to fill out a federal background check form. In response to a question on the form about whether he was using drugs, Mr. Biden said he was not — an assertion that prosecutors concluded was false.

The first two charges against Mr. Biden are essentially the same — that he lied about his drug use to illegally obtain the weapon, and that he falsely claimed that he was not “addicted to any stimulant, narcotic drug, and any other controlled substance” on the federal form, known as a 4473.

The third charge, illegal possession of the gun while under the influence of drugs, stems from the time he had the weapon. Hallie Biden, his brother Beau’s widow — and his romantic partner at the time — eventually discovered the gun and threw it into a dumpster.

The section of federal law cited in the indictment, 18 U.S. Code § 922, is the main statute used to define who can and cannot possess a firearm. It bars drug users, people convicted of felonies whose punishment exceeds a one-year prison sentence, fugitives from justice, people judged to be “mentally defective,” and those receiving dishonorable discharges from the military.

How common is this type of prosecution?

A substantial percentage of those accused of lying on a federal firearms application, like Mr. Biden has been, are not indicted on that charge unless they are also accused of a more serious underlying crime, current and former law enforcement officials said. Most negotiate deals that include probation and enrollment in programs that include counseling, monitoring and regular drug testing.

“It is rare as a stand-alone,” said John P. Fishwick Jr., who served as U.S. attorney for the Western District of Virginia from 2015 to 2017. “These charges are usually brought against convicted felons who illegally possess a gun or who commit a violent or drug-related charge.”

Prosecutions for lying to a dealer are relatively rare, averaging fewer than 300 per year. There were some 25 million to 30 million background checks performed annually around the time of Mr. Biden’s gun purchase, according to statistics obtained by The Washington Post.

Charges of illegal firearms possession are much more common. But they too are most often used as an add-on, to leverage plea deals or to ensure that a defendant is convicted on at least one charge if there are doubts that they will be convicted on an underlying charge, Mr. Fishwick and other former prosecutors said.

In May, for example, when more than 20 people in Savannah were sentenced to from 10 months to 12 years in prison after pleading guilty to illegal firearms possession, all of them had criminal records or were caught in the act of committing another crime.

When officials with the federal Bureau of Alcohol, Tobacco, Firearms and Explosives reviewed Hunter Biden’s gun application several years ago, they believed the case most likely would have been dropped if the target were a lesser-known person — because the gun had not been used in a crime and Mr. Biden had taken steps to get and stay sober, according to a former law enforcement official familiar with the situation.

What happens now?

No date has been set for Mr. Biden’s arraignment in federal court in Wilmington.

It is possible the case will go to trial. It is also possible that a federal judge will ask the two parties to work out a plea deal similar to the one Mr. Biden’s lawyers had hashed out with the top federal prosecutor in Delaware, David C. Weiss, an arrangement known as a pretrial diversion agreement.

Under that doomed deal, the Justice Department agreed not to prosecute Mr. Biden over the handgun purchase, contingent on Mr. Biden remaining drug-free for 24 months and never owning a firearm again.

The agreement brokered by Mr. Weiss, who was made special counsel after the deal collapsed at a disastrous court hearing in late July, was more favorable to Mr. Biden than any agreement he would receive at this point. According to Mr. Biden’s lawyer at the time, the deal included a sweeping guarantee of immunity from prosecution on the firearms case and any potential charges stemming from Mr. Biden’s work for foreign companies.

Abbe Lowell, a lawyer for Mr. Biden, is pressing the court to honor the previous agreement, arguing that the indictment is “barred” by the old deal, whose conditions he asserts are still operative. The judge in the case has yet to rule on his request.

Republicans portrayed the original plea agreement as a “sweetheart deal,” and proof that the Justice Department was seeking to protect the president’s son, even though Mr. Weiss was appointed to investigate the case by former President Donald J. Trump. Speaker Kevin McCarthy has cited the case as one of the reasons that House Republicans are opening an impeachment inquiry into President Biden.

What is the constitutional issue?

Gun rights activists argue that prosecuting substance abusers for buying or owning guns — especially those, like Mr. Biden, who claim to be sober for long periods of time — violates the Second Amendment right to bear arms.

There have been calls in recent years to alter or remove the drug question from the federal firearms application, especially when it comes to marijuana use, but Congress has not amended federal firearms or drug laws, and federal officials have not weakened their regulations.

In May, the A.T.F. held firm on that position, warning cannabis users in Minnesota that they were barred from buying guns or ammunition despite the state’s easing of marijuana restrictions.

But a 2022 Supreme Court ruling has spawned an all-fronts effort by gun rights advocates to roll back federal gun laws. The case, New York State Rifle & Pistol Association v. Bruen, vastly expanded people’s right to arm themselves in public.

One case Hunter Biden’s team has cited is a challenge to the criteria used in the federal firearms background check system, pending before the U.S. Court of Appeals for the Third Circuit, which includes Delaware.

If that lawsuit succeeds, it could undermine the legal foundation of his prosecution. If the court finds that it is unconstitutional to base an illegal firearm possession charge on a violation of the law banning sales to people who have been addicted to drugs, the two other charges lodged against Mr. Biden — making false claims about drug use to obtain the gun — would likely collapse too, said Andrew A. Weissmann, a former federal prosecutor and F.B.I. official.

“It is remarkable for Special Counsel Weiss to bring theses charges, not only because they are exceedingly rare, but bringing them now when the issue involving whether the statute is constitutional is a lively prospect.” said Mr. Weissmann, who led Robert Mueller’s investigation of the Trump campaign’s connections to Russia.