Wilmington, Delaware - President Joe Biden's son Hunter asked a judge Wednesday to issue a subpoena to Donald Trump, claiming an investigation that led to gun charges against him was politically motivated.

In a filing with a US District Court in Delaware, Hunter Biden (53) is seeking documents and records from Trump, his former attorney general Bill Barr, former acting attorney general Jeffrey Rosen, and former acting deputy attorney general Richard Donoghue.

Hunter Biden pleaded not guilty last month to three felony charges stemming from his purchase of a .38-caliber Colt Cobra revolver in 2018 when, by his own admission, he was addicted to drugs.

He is charged with illegally possessing the handgun and two counts of making false statements for claiming on forms required for the gun purchase that he was not using drugs at the time.

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In the court filing seeking subpoenas, his lawyer, Abbe Lowell, said there was evidence Trump had applied "incessant, improper, and partisan pressure" on Barr and the other top Justice Department officials to investigate Hunter.

"Mr. Trump has made a plethora of concerning public statements calling for an investigation or possible prosecution of Mr. Biden, both while in office and since leaving," Lowell said.

He cited numerous tweets by Trump and a passage from a recent book by Barr, who served as attorney general under the former Republican president until resigning in December 2020.

In the book, Barr says Trump asked him in October 2020 about the status of an investigation into Hunter Biden.

"Dammit, Mr. President, I am not going to talk to you about Hunter Biden. Period!" Barr says he responded angrily.

Rosen and Donoghue took over the Justice Department's leadership following Barr's resignation, serving until Trump left the White House in January 2021.

Hunter Biden's legal troubles and controversies – which extend to accusations from Republican politicians that he engaged in corrupt business practices in China and Ukraine – are a drag on his father's political standing as he seeks a second term in 2024 in a possible rematch against Trump, the Republican presidential frontrunner.

Republicans have opened an impeachment inquiry in Congress into what they claim is a Biden family criminal conspiracy but have provided no evidence that the president did anything wrong.

In July, a plea bargain between Hunter Biden and prosecutor David Weiss -- which would have erased the gun charges while Biden pleaded guilty to two tax charges and avoided prison – fell apart.

Hunter Biden has not been charged with any crimes related to his foreign business dealings, despite the Republican allegations.

Hunter Biden is a Yale-trained lawyer and lobbyist-turned-artist, but his life has been marred by alcoholism and crack cocaine addiction.