The justices said Tuesday they will take up appeals asking the court to strike down bans on the AR-15 and similar semiautomatic firearms in Connecticut and the Chicago area.
In 1927, Congress passed a law barring the USPS from mailing concealable firearms unless they were from licensed dealers in an effort to curb crime.
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.
Authorities say two parents were arrested after guns were discovered at elementary schools in Nash County and Fayetteville.
"Whoever is responsible for this, and if it was a mistake, just come out and say it was a mistake."