Attorneys for the president’s son say an FBI informant’s lies have “infected” the case against their client.

Hunter Biden faces federal charges for having failed to pay his taxes on time and for illegally owning a gun when he was addicted to crack cocaine. A plea deal and diversion agreement collapsed last summer over a disagreement about Biden’s immunity from further charges.

In a court filing on Tuesday, Biden’s attorneys suggested prosecutors abandoned the plea deal because they believed they might be able to charge Biden with a more serious crime. The bribery allegation came from an FBI informant named Alexander Smirnov, whom the government has just accused of making the whole thing up.

“It now seems clear that the Smirnov allegations infected this case,” Biden’s legal team, led by Abbe Lowell, said in a court filing in Delaware, adding in a footnote that prosecutors had “taken Mr. Smirnov’s bait of grand, sensational charges.” The motion asked the court to make prosecutors hand over more evidence ahead of a trial.

Smirnov told his FBI handler in 2020 that the head of the Ukrainian gas company Burisma, which employed Hunter Biden on its board, had paid both Joe and Hunter Biden $5 million in bribes. In June, Republicans obtained and released a raw FBI file describing the allegation, which became a major part of their impeachment inquiry against the president.

Last week, however, the government said they’d poked holes in Smirnov’s story and that he fabricated the allegation because he opposed Biden’s candidacy for president. The charges were filed by David Weiss, the same prosecutor overseeing the case against Biden. In the indictment against Smirnov, prosecutors said the FBI asked Weiss for help investigating the bribe claim in July, shortly after Republicans made it public.

The allegations against Smirnov are a bombshell that could potentially destroy the impeachment case against President Biden. His son’s attorneys hope Smirnov’s fabrication could also taint the prosecution of their client, though it’s not clear if it will have the same impact.

In their court filing on Tuesday, Biden’s attorneys claimed prosecutors started looking into Smirnov’s allegation “just days before” the fateful July 26 hearing where Biden’s plea deal fell apart. According to the transcript, the disagreement arose when prosecutors said the plea deal would not prevent them from bringing charges under the Foreign Agents Registration Act. Biden’s attorneys wanted him free and clear.

The bribery allegation did not come up during that meeting, however, and Weiss’s team hasn’t mentioned it in any of its court filings.

The Justice Department elevated Weiss last year to special counsel status so he could bring charges against Biden in other states; he’s now pursuing the gun charge in Delaware and the tax charges in California. Republicans in Congress have also clamored for Biden to be charged with acting as an unregistered foreign agent.

Biden has openly admitted to habitually using crack cocaine when he bought a gun in 2018, meaning he lied on the standard federal form asking gun purchasers to declare they’re not addicted to a controlled substance. And he has not denied that he failed to pay his taxes on time. But his legal team has argued that prosecutors would not have brought the charges against a normal person and that the president’s son has been singled out for political reasons.

“Our motions expose the special counsel has gone to extreme lengths to bring charges against Mr. Biden that would not have been filed against anyone else,” Lowell said in a statement on Tuesday. “Prosecutors reneged on binding agreements, bowed to political pressure to bring unprecedented charges, overreached in their authority, ignored the rules and allowed their agents to run amok, and repeatedly misstated evidence to the court to defend their conduct.”