President Donald Trump criticized a sheriff’s deputy who was present during a massacre at a Florida high school last week but stayed outside the building, calling him a coward.

The deputy, Scot Peterson, "certainly did a poor job," Trump said, adding that Peterson "didn’t react properly under pressure" or was "a coward," the president told reporters as he left the White House Friday morning.

"What he did, he’s trained his whole life, there’s an example, but when it came time to get in there and do something, he didn’t have the courage or something happened," Trump said.

A former student armed with an AR-15-style rifle killed 17 people at Marjory Stoneman Douglas High School in Parkland, Florida, on Feb. 14. Peterson was assigned to the school as a resource officer and on the campus when the shooting began.

Trump is calling the episode "a real shot to the police department" and says this "could have been prevented."

Trump returned to the theme later in a speech at the Conservative Political Action Conference, arguing that teachers, coaches and other school staff would be more likely to risk their lives to fight an attacker than Peterson or other guards with less of a personal connection to students.

"I’d rather have someone who loves their students and wants to protect their students," Trump told the gathering of conservative political activists. "A teacher would have shot the hell out of him before he knew what happened."

Trump has proposed training and arming some teachers to deter and fight assailants.

“You have to have a certain amount of offensive power” within schools, Trump said. The National Rifle Association, he said, “wants to do the right thing. I’ve been speaking to them and they do want to do the right thing.”

The NRA has so far objected to one of Trump’s proposals, to raise the legal age to buy a semiautomatic firearm to 21. It also opposes many Democratic proposals to restrict gun ownership, including limits on the size of magazines or a ban on semiautomatic rifles of the sort Cruz used in his attack.

Peterson, the school resource officer at the campus, never went inside to engage the gunman and is under investigation, Broward County Sheriff Scott Israel said at a news conference on Thursday, according to the Associated Press.

Israel said Peterson should have “went in, addressed the killer, killed the killer,” according to the AP. Instead, the officer took up a position in view of the western entrance of the building while the gunman, Nikolas Cruz, conducted his rampage.

The sheriff said he was “devastated, sick to my stomach,” over the deputy’s inaction, the AP reported. “There are no words.”

Peterson chose to resign after being suspended without pay, Israel said.