Federal law prohibits people under felony indictment from buying guns.
The late-night host rips the former president for "a remarkably stupid and dangerous idea."
The chief correspondent was wounded in his lower back while the cameraman took two rounds to his body armour.
The US president has been pressured to act after two major mass shootings took 18 lives in March.
The gunman is seen on surveillance video walking up to the patrol car and firing through the passenger side window before running away.
Some buyers are worried about potential lawlessness. Others want to stock up in case prices jump.
30 people are dead in Texas and Ohio after the massacres which happened within just 13 hours of each other.
A man was arrested after authorities found the massive cache of weapons at a home in an upscale neighbourhood popular with celebrities.
Consultation on the move is at an early stage, but the force has denied it will become routine.
Police launch an attempted murder investigation.