Questions are swirling surrounding security at the White House Correspondents' Dinner on Saturday after shots rang out when an alleged gunman tried to charge a security checkpoint outside the event. The annual gala was attended by 2,500 guests, including President Trump and top administration officials.

"I was perplexed even before the incident about what I saw in security," Aaron MacLean, a CBS News national security analyst and military veteran, told "CBS Mornings" in an interview on Monday.

MacLean attended the dinner for the first time this year and said his ID was not checked "at any point in the evening."

"To get into the hotel all I had to do was show a screenshot of an invitation," he said.

MacLean said he thinks the attack renews questions over training and procedures for the Secret Service.

"You can't just look at something like this and pat yourself on the back that this unserious person didn't succeed," he said.

Mr. Trump and first lady Melania Trump were safely evacuated from the event and none of the attendees were seriously injured, officials said. One Secret Service agent was injured by gunfire in the attack, but has since been released from a hospital.

"Ask yourself what if it had been four or five very serious people, not one unserious person. Is 10 seconds to get anyone to protect the president good enough, 20 seconds to get him off the stage? I don't think so," he said.

Inside the dinner, MacLean described Secret Service agents who were visible as "not very close to the president."

"There were more people behind that curtain, but as we saw it took them time to react. Once the incident happened it was a full two minutes or so before anyone came to get the secretary of war," MacLean said. He was with Defense Secretary Pete Hegseth, who he described as alert and "assessing what was going on in the room" when the shots were fired.

What's known about the alleged gunman

Law enforcement was able to stop and arrest the suspect, identified as 31-year-old Cole Thomas Allen of Torrance, California. He was armed with a shotgun, a handgun and knives, officials said.

Acting Attorney General Todd Blanche said Sunday on "Face the Nation with Margaret Brennan" that investigators believe Allen was targeting Trump administration officials.

According to authorities, Allen was staying at the Washington Hilton Hotel, where the dinner was hosted, and used an interior stairwell to bypass areas of the hotel that were heavily monitored.

"This gunman was clearly mentally unstable, his tactical plan was a bit of a joke. That doesn't mean he couldn't have done harm," MacLean said. "We're very lucky and there was a lot of individual valor on the part of the agents involved that stopped him."

Secret Service Deputy Director Matthew Quinn posted a statement over the weekend about the incident, saying: "Tonight, a coward attempted to create a national tragedy. He underestimated the protective capabilities of the U.S. Secret Service and was stopped at first contact."

The FBI is conducting a criminal investigation into the attack. Allen is set to appear in federal court on Monday for an arraignment.