• Lawyers for Hunter Biden want to subpoena documents from Donald Trump, former Attorney General Bill Barr, and other former Department of Justice officials.
• Biden wants to see if there is evidence that Trump or DOJ officials exerted pressure to launch the criminal investigation into his taxes and foreign business dealings.
• The son of President Joe Biden is charged with crimes related to possessing a handgun while being a drug user.

Lawyers for Hunter Biden raised the prospect that he is the victim of "vindictive" prosecution Wednesday as they asked a federal judge to issue subpoenas demanding documents from former President Donald Trump, his ex-attorney general Bill Barr, and two other former top Department of Justice officials.

Biden's attorneys said the documents are needed for the son of President Joe Biden to prepare his defense in the criminal case where he is charged with possessing a handgun while being a drug user.

The information that Hunter is seeking could answer "whether this investigation or prosecution arose" because of any executive branch official, such as Trump or Justice Department officials, "placing undue pressure on government officials" to probe Hunter, the filing said.

"Mr. Biden seeks specific information from three former DOJ officials and the former President that goes to the heart of his defense that this is, possibly, a vindictive or selective prosecution arising from an unrelenting pressure campaign beginning in the last administration, in violation of Mr. Biden's Fifth Amendment rights under the Constitution," the filing said.

The criminal probe of Hunter that led to the pending case in Delaware federal court began in late 2018, during the Trump administration.

That investigation was originally focused on Hunter's income taxes and foreign business dealings.

In addition to requesting a subpoena for Trump and Barr, Hunter's lawyers also want a judge to issue subpoenas to former acting U.S. Attorney General Jeffrey Rosen, and to Richard Donoghue, who ended up serving as Rosen's deputy AG after holding other DOJ positions.

"Public reporting reveals certain instances that appear to suggest incessant, improper, and partisan pressure applied by then President Trump to Messrs. Rosen, Donoghue, and Barr in relation to an investigation of Mr. Biden," the court filing says.

"For example, on December 27, 2020, then Deputy Attorney General Donoghue took handwritten notes of a call with President Trump and Acting Attorney General Rosen, showing that Mr. Trump instructed Mr. Rosen and Mr. Donoghue to 'figure out what to do with H[unter] Biden' and indicating Mr. Trump insisted that 'people will criticize the DOJ if he's not investigated for real."

Hunter for years has been the focus of attention and criticism by Trump and his Republican allies in Congress and elsewhere who accuse him of being involved in corrupt activities that have allegedly implicated President Biden.

That criticism grew after David Weiss, the U.S. Attorney for Delaware, negotiated a plea deal with Hunter's lawyers that would have seen Hunter plead guilty to misdemeanor tax charges while accepting a pre-trial diversion agreement that eventually was expected to lead to the dropping of any gun-related charge.

That plea deal, which included a recommendation of no jail time for Hunter, fell apart during a court hearing this summer when a judge questioned its terms.

Weiss soon afterward was appointed special counsel in the case by Attorney General Merrick Garland.

Weiss dropped the tax charges against Hunter with the understanding that those charges and other similar ones might be filed in another federal court. And he obtained an indictment against Hunter on gun-related charges.

The prosecutor has been criticized by Trump and his allies for the initial plea deal and for not charging Hunter with more serious crimes.

Hunter's lawyers, in turn, argue that the current gun charges are barred by the diversion agreement.