Four arrests were made and three guns were recovered over the weekend after reports of a "teen takeover" at a northwest Indiana beach, police said.
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.
The first count of attempting to assassinate the president carries a maximum sentence of life in prison if convicted.
A parent notified police after seeing the suspect walking around the school with a handgun on his hip, the sheriff's office said.
The Secret Service Presidential protection mission dates back to 1901; it was formalized after the assassination of President William McKinley.