WASHINGTON — A federal district judge in Delaware refused Friday to throw out a federal gun case against Hunter Biden, rejecting the president’s son’s claim that he is being prosecuted for political purposes as well as other arguments.

Judge Maryellen Noreika’s ruling increases the prospect that the president’s son could face trial in the case as early as June, in the midst of his father’s reelection campaign. 

His efforts to scuttle the other criminal case he faces in California involving tax allegations have also failed.

Judge Norieka denied several defense requests to dismiss the case charging Mr. Biden with lying about his drug use in October 2018 on a form to buy a gun that he kept for about 11 days.

His lawyers had argued the case was politically motivated and asserted that an immunity provision from an original plea deal that fell apart still holds. They had also challenged the appointment of Delaware’s United States attorney, David Weiss, as special counsel to lead the prosecution.

Judge Noreika, who was appointed to the bench by President Trump, has not yet ruled on a challenge to the constitutionality of the gun charges.

Mr. Biden has pleaded not guilty. A representative for his legal team didn’t immediately respond to a request for comment Friday.

The president’s son has acknowledged struggling with an addiction to crack cocaine during that period in 2018, but his lawyers have said he didn’t break the law and another nonviolent, first-time offender would not have been charged.

The yearslong investigation had looked ready to wrap up with a plea deal last year, but the agreement imploded after a judge raised questions about it. Mr. Biden was subsequently indicted.

Under the deal, he would have gotten two years’ probation after pleading guilty to misdemeanor tax charges. He also would have avoided prosecution on the gun charge if he stayed out of trouble. He was subsequently indicted.

His attorneys have argued that prosecutors bowed to political pressure to indict the president’s son amid heavy criticism of the plea deal from Mr. Trump and other Republicans.

Prosecutors countered the evidence against him was “overwhelming,” including cocaine residue found in the pouch where he stored his gun, and noted that charges had been filed during the presidency of his father.

Judge Norieka said in her ruling that Mr. Biden’s team provided “nothing concrete” to support a conclusion that anyone actually influenced the special counsel’s team.

“The pressure campaign from Congressional Republicans may have occurred around the time that Special Counsel decided to move forward with indictment instead of pretrial diversion,” she wrote. 

However, she added, “the Court has been given nothing credible to suggest that the conduct of those lawmakers (or anyone else) had any impact on Special Counsel.” She called it “all speculation.”

The judge also knocked down the defense’s claim that the case must be dismissed because the diversion agreement — the part of the prior deal that would have allowed the gun case to be wiped from his record — was still valid. 

The judge said the probation office never actually signed to approve the diversion agreement, which was necessary for it to go into effect.

Mr. Biden fils faces separate tax counts in Los Angeles alleging he failed to pay at least $1.4 million in taxes over three years while living an “extravagant lifestyle,” during his days of using drugs. 

The judge overseeing that case knocked down eight motions to dismiss those charges earlier this month. The younger Mr. Biden’s lawyers told the court Friday that they will appeal those rulings.

That trial is also scheduled to begin in June.