Prosecutors seek to corroborate testimony from three of his former romantic partners to argue he was still addicted to crack cocaine when he bought the gun.
Prosecutors allege that Mr. Biden was in the grips of crack cocaine addiction when he bought the gun, pointing to potentially self-incriminating statements.
Both allege that Mr. Biden was a functioning crack cocaine addict, refuting the defense argument that an addict could not have functioned enough to buy the gun.
The program, which provides funds to residents of areas contaminated by fallout and to workers mining radioactive materials, is set to expire on June 10.