WILMINGTON, Delaware (Reuters) -The ex-wife of U.S. President Joe Biden’s son Hunter Biden is expected to testify on Wednesday about the younger Biden’s drug use, which prosecutors contend he lied about to illegally buy a gun.

Prosecutors told jurors hearing the historic first trial of a U.S. president’s child that evidence will show Hunter Biden knowingly lied about his drug use on screening paperwork when he purchased a revolver in October 2018.

Jurors were shown text messages, bank records and clips of the audiobook version of Hunter Biden’s memoir that prosecutors say prove he was routinely using crack around the time he bought the gun, including the day after he made the purchase.

“Addiction is not a crime. Lying is,” prosecutor Derek Hines said.

His defense lawyer has countered that Hunter Biden was not using drugs at the time and did not intend to deceive. He pressed an FBI agent to acknowledge that prosecutors’ evidence of addiction came before or after the gun ownership.

Hunter Biden, 54, has pleaded not guilty to three felony charges accusing him of failing to disclose his use of illegal drugs when he bought the gun and of illegally possessing the weapon for 11 days.

The trial follows another historic first – last week’s criminal conviction of Donald Trump, the first U.S. president to be found guilty of a felony. Trump is the Republican challenger to Joe Biden, a Democrat, in the Nov. 5 election.

Hines told jurors they would next hear from Hunter Biden’s ex-wife Kathleen Buhle, as well as his former girlfriend Zoe Kestan, and Hallie Biden, the widow of his late brother Beau Biden. All three can speak to Hunter Biden’s years-long struggles with drugs and alcohol, Hines said.

On Wednesday, Hunter Biden’s attorney Abbe Lowell elicited testimony from an FBI agent acknowledging the messages about drug use preceded a return to Delaware after a drug treatment stint in California or were sent months after the gun was taken.

Erika Jensen, the FBI agent who was called by the prosecution on Tuesday, acknowledged Hunter Biden’s messages when he returned to Delaware after a drug treatment stint in California lacked drug references such as “party favor” or pictures of drug paraphernalia.

Lowell also tried to show that while Hunter Biden was making large cash withdrawals, which prosecutors said was evidence of drug purchases, he was also supportive of a “sober companion” whose treatment cost thousands of dollars weekly.

Trump is due to be sentenced on July 11 after being convicted by a jury in state court in New York last Thursday of 34 felony counts of falsifying documents to cover up hush money paid to a porn star to avoid a sex scandal shortly before the 2016 U.S. election.

He has pleaded not guilty in three other pending criminal cases, two related to his efforts to overturn his 2020 election loss to Biden and one accusing him of unlawfully keeping classified national security documents after leaving office in 2021.

(Reporting by Jack Queen and Tom Hals; Editing by Scott Malone, Stephen Coates and Nick Zieminski)