Hunter Biden’s attorney is asking the federal judge overseeing his federal gun case to dismiss the criminal charges against him, arguing that an earlier agreement with prosecutors gives him immunity.

The motion was one of four Biden filed Monday in Delaware federal court seeking to have the felony gun charges tossed. Special counsel David Weiss, who brought the gun charges against Biden in September, recently hit the president’s son with numerous tax-related charges in federal court in California.

Both cases spring from the same investigation that led to a failed plea agreement in July. Under the terms of that deal, which fell apart under scrutiny from the judge, Biden would have pleaded guilty to two misdemeanor tax charges in return for a sentence of six months probation, while a felony gun charge could have been dismissed in two years.

Biden attorney Abbe Lowell, who acknowledges that the plea deal was subsequently withdrawn by prosecutors, has said that the agreement pertaining to the felony gun charge was already in effect at the time of the July hearing, and therefore prosecutors are barred from bringing related charges.

Prosecutors maintain the agreement never took effect because it didn’t have the necessary approval from the Probation Office.

Lowell pushed back on prosecutors’ position in one of Monday’s filings, saying the agreement “required execution and approval from the parties—not by Probation.” There “is no provision that says Probation must sign the Diversion Agreement for it to be effective,” he wrote.

In another filing, Lowell argued the case should be dismissed because Biden is the victim of “selective and vindictive prosecution.” He said the investigation into his client had been “polluted with politics” since Weiss launched it during the Trump administration.

He went on to say that former President Donald Trump started accusing his political rival’s son of corruption in 2018 “without any evidence,” and suggested that Weiss bowed to pressure from House Republicans in recent months and over-charged his client.

“As a holdover from the Trump Administration, Mr. Weiss faces political pressure from his own party to pursue Mr. Biden more aggressively than similarly situated individuals and to do so for vindictive reasons,” the filing said.

In another motion Monday, Lowell argued that the specific charges against Biden, which are all related to his lying about his drug use when he bought a gun in 2018, are unconstitutional due to recent rulings in other courts relaxing gun restrictions.

“Because persons protected by the Second Amendment can no longer be denied gun ownership due simply to past drug use—a practice inconsistent with this nation’s historical tradition on firearm regulation—any false statement by Mr. Biden concerning his status as having used a controlled substance no longer concerns ‘any fact material to the lawfulness of the sale’ of a firearm,” the filing said. “Quite simply, asking about Mr. Biden’s status as a user of a controlled status is constitutionally irrelevant to whether he can be denied his Second Amendment right to gun ownership.”

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The fourth filing on Monday argued that the case should be dismissed because U.S. Attorney General Merrick Garland should have chosen a special counsel from outside the Justice Department, saying DOJ regulations required him to do so.

The filings also include an affidavit from former Biden lawyer Christopher Clark, who said despite what prosecutors said in court at the July hearing where the plea agreement imploded, they had knowingly agreed to a provision that also gave Biden immunity from any other tax-related crimes during the period surrounding his alleged gun violation.

Clark also said the Delaware U.S. Attorney’s Office, which Weiss heads, had agreed to language in a press release that said the investigation into Biden was “resolved,” and that one of the prosecutors had assured him there “was not another open or pending investigation.” At one point during the hearing, however, the judge asked if the investigation was ongoing and Weiss said it was.

In a statement Monday, Lowell said the charges against his client“are unprecedented, unconstitutional and violate the agreement the U.S. Attorney made with Mr. Biden and DOJ’s own regulations.”

“This is not how an independent investigation is supposed to work, and these charges should be dismissed,” Lowell added.

The special counsel’s office did not immediately respond to a request for comment on the filings. Weiss has until Jan. 16 to file a response with the court.

Lowell is likely to make some of the arguments in federal court in California, where Biden was indicted last week on nine tax-related charges, including three felony counts, which fall in the same time period.

“Between 2016 and October 15, 2020, the Defendant spent this money on drugs, escorts and girlfriends, luxury hotels and rental properties, exotic cars, clothing, and other items of a personal nature, in short, everything but his taxes,” the indictment says.

Biden has yet to be arraigned or enter a plea in that case.

In a statement Thursday, Lowell said, “Based on the facts and the law, if Hunter’s last name was anything other than Biden, the charges in Delaware, and now California, would not have been brought.”