Lawyers for the man accused of killing conservative activist Charlie Kirk are trying to sow doubt about the case.
Trump's Republican administration alleges the ban violates the Constitution's Second Amendment right to bear arms.
Pirro said there is evidence that buckshot from a shotgun carried by alleged White House Correspondents' Dinner attacker was "intertwined with the fiber" of a bulletproof vest worn by a Secret Service officer.
Cole Allen, the suspect in the White House Correspondents' Association Dinner shooting, conceded to remain detained.
The first count of attempting to assassinate the president carries a maximum sentence of life in prison if convicted.
California Attorney General Rob Bonta on Tuesday highlighted what he called historic progress in the state's fight against gun violence.