It was Saturday night, and Palm Beach’s tony Mar-a-Lago Club was packed. There was a wedding reception in the ballroom. There was a full house for dinner on the terrace.

And at one table on the terrace, there was the president and the leader of a major U.S. ally, hashing out a national security problem in the open air.

“Someone opened up a laptop, and at the table . . . a group of Japanese people stood around the prime minister and Donald, and they were all looking at the laptop,” said Jay Weitzman, a member of President Trump’s Mar-a-Lago Club and founder of the Pennsylvania-based parking management company Park America. He was sitting three tables away from Trump and Japanese Prime Minister Shinzo Abe on Saturday evening.

“Whoa,” Weitzman remembered thinking. “What’s going on?”

“Turns out, it was a missile launch,” he said Monday.

Richard DeAgazio's post on Facebook.

As Weitzman and other patrons watched Saturday evening, Trump and Abe remained at the table and discussed their response to a ballistic missile test by North Korea. While waiters came and went — and while one club member snapped photos — the two leaders reviewed documents by the light of an aide’s cellphone.

That strange scene — in which Trump turned his table into an al fresco situation room — astounded White House veterans, who were used to presidents retiring to private, secured settings to hash out such an event.

Trump became president, in part, because of Democrat Hillary Clinton’s neglect of information security. During the 2016 campaign, Trump repeatedly called for Clinton to be jailed — and his crowds at rallies often chanted “Lock her up!” — for her use of a private email server to handle government business while she was secretary of state.

Now, Trump is drawing fire from Democrats for his own seemingly loose attitude toward information security. He has continued to use an insecure cellphone, according to the New York Times. He may have left a key to classified information on his desk while visitors were in the Oval Office, according to a tweet from a Democratic senator.

And now, Trump has used his bustling club in Palm Beach, Fla., as a “winter White House,” except that, unlike the actual White House, the club is full of other people.

Sean Spicer, the White House press secretary, told reporters Monday that “no classified material” was shared at the table at Mar-a-Lago and that Trump had been briefed in a secure location both before and after dinner.

The scene was first described by CNN. On Monday, Democrats blasted Trump for his handling of the moment.

1 of 83 Full Screen Autoplay Close Skip Ad × See what President Trump has been doing since taking office View Photos The new president is expected to make his mark on an aggressive legislative agenda. Caption The beginning of the president’s term has featured controversial executive orders and frequent conflicts with the media. March 17, 2017 President Donald Trump, first lady Melania Trump and their son, Barron, walk to Marine One at the White House en route to Mar-a-Lago in Palm Beach, Fla. Jabin Botsford/The Washington Post Buy Photo Wait 1 second to continue.

“There’s no excuse for letting an international crisis play out in front of a bunch of country club members like dinner theater,” Rep. Nancy Pelosi (Calif.), the leader of House Democrats, wrote in a tweet.

Separately, two Senate Democrats from the Homeland Security Committee, Claire McCaskill (Mo.) and Thomas R. Carper (Del.), wrote to Defense Secretary Jim Mattis, who oversees the agency that protects the president’s communications. McCaskill and Carper said they were concerned about media reports that Trump is still using his old Android phone to send Twitter messages.

McCaskill and Carper said that if a foreign power was able to hack that phone, it could be turned into an always-on listening post in the president’s pocket.

“The national security risks of compromising a smartphone used by [the president] are considerable,” the senators wrote.

Last week, Sen. Martin Heinrich (D-N.M.) tweeted an Associated Press photo showing Trump with the chief executive of Intel standing by a stack of papers on Trump’s desk along with a black bag and a key in sight. “Never leave a key in a classified lockbag in the presence of non-cleared people,” Heinrich wrote.

It is hard to recall any other instance in recent U.S. history when the president seemed to handle an urgent national security matter in a public place.

On Sept. 11, 2001, of course, President George W. Bush learned of that day’s terrorist attacks while he was reading a book to children at a Florida elementary school. Bush continued reading for at least five minutes before being whisked away on Air Force One to a secure location.

In Barack Obama’s White House, two former aides said, a situation like the North Korean missile test might have been handled similarly: the president would be given a note with the news, then taken to a secure room to discuss a response.

Pete Souza, who was Obama’s White House photographer, posted a photo Monday that showed Obama huddling with national security advisers in a private space during a 2011 trip to El Salvador.

“When we were on the road, national security discussions and head of state phone calls were conducted in a private, secure location set up on-site. Everyone had to leave their Blackberry outside the area,” Souza wrote.

The Mar-a-Lago Club, which Trump has run since 1995, includes tennis and beach facilities for its members and rents its ballroom out for weddings and galas open to nonmembers.

Trump has an apartment at the club. Club members said that the president seems at ease there, among people who have known him for years — and away from the protests and stresses of his new job. “He’s in a safe space,” said Mar-a-Lago member Robin Bernstein, an insurance executive.

Saturday night, as guests streamed into Mar-a-Lago for dinner and the wedding reception, a parking lot near the club had been converted into a ­security-check area for vehicles entering the estate. A string of BMWs, Mercedes and other high-end vehicles were backed up waiting to get through the checkpoint, which was staffed by Secret Service agents and officers from the Palm Beach County Sheriff’s Office.

Inside the club, Trump and Abe entered the dining terrace to a standing ovation, club members told The Washington Post. The two leaders and their wives sat down on the noisy terrace, among other diners.

Richard DeAgazio, a retired investor and club member from the Boston area, was about six tables away. Already that day, his status as a Mar-a-Lago member had given him unprecedented access to the president: He had snapped pictures of Trump and Abe golfing and taken a photo with White House strategist Stephen K. Bannon.

During dinner, DeAgazio got a text: a friend asking him if he was aware of the North Korean missile test.

He looked over at the president’s table.

“That’s when I saw things changing, you know,” DeAgazio recalled in a telephone interview. DeAgazio said a group of staffers surrounded the two world leaders: “The prime minister’s staff sort of surrounded him, and they had a little powwow.”

As Trump and Abe turned their dinner table into an impromptu situation room, DeAgazio continued taking pictures, and he posted them on Facebook that night.

[Should President Trump be spending weekends at Mar-a-Lago?]

“The President receiving the news about the Missile incident from North Korea on Japan with the Prime Minister sitting next to him,” DeAgazio wrote as the caption for a photo he posted on Facebook at 9:07 p.m. Eastern time Saturday.

“HOLY MOLY !!!” De Agazio wrote later, posting more photos of the scene. “Wow . . . the center of the action!!!”

DeAgazio told The Post that after Trump and Abe had spoken for a few minutes, they left the open terrace and spent about 10 minutes in private before conducting a joint news conference at about 10:30 p.m. Later, he said, Trump and first lady Melania Trump returned to listen to music on the terrace, which faces the Intracoastal Waterway, and shake hands and schmooze with members and guests at the club — all of whom had paid Trump’s business to be there (or been paid-for by their hosts).

DeAgazio said he was impressed with how the president handled the situation.

“There wasn’t any panicked look. Most of the people [on the terrace] didn’t even realize what was happening,” DeAgazio said. “I thought he handled it very calmly, and very presidentially.”

[Trump ran a campaign based on intelligence security. That’s not how he’s governing.]

Weitzman, the parking garage entrepreneur, said he didn’t notice any weariness or concern in the president’s face, even after the news from North Korea. He said Trump was jovial: The president, for instance, complimented Weitzman’s son-in-law on his recent weight loss.

“It’s amazing,” Weitzman said. “You know, the president of the United States comes over and says, ‘You lost a little weight. How ya doing?’ ”

DeAgazio, the Boston retiree, said he was impressed that Trump had not gotten up from the table immediately when the North Korean news broke.

“He chooses to be out on the terrace, with the members. It just shows that he’s a man of the people,” DeAgazio said.

Membership at the Mar-a-Lago Club now requires a $200,000 initiation fee — a fee that increased by $100,000 after Trump was elected.

DeAgazio said he wasn’t worried about the national security implications of Trump’s al fresco discussion with Abe. He said he was sure they had not been overheard.

“You don’t hear anything. You can’t hear” because of the background music and other diners’ chatter, DeAgazio said. “I mean, I can barely hear what’s going on at my table.”

This story has been updated to correct the amount of time former president George W. Bush continued reading to school children after being informed of the Sept. 11, 2001 terrorist attacks.

John Wagner, Philip Bump and Abby Phillip contributed to this report.