It’s unclear who, exactly, was the first to camp out in front of Deon’s Restaurant on Circuit avenue in Oak Bluffs early Tuesday evening, hoping to spot President Obama and First Lady Michelle Obama. And it wasn’t clear, even among those there, where the idea that the President was coming even started.

“The Secret Service was in there today,” said one onlooker, wearing a Bo-bama T-shirt, in honor of the First Dog.

“He’s friends with the owner. They brought in a second chef from New York,” said Marie Carpizzo of Fall River.

“They set up a special table for him,” added Libby Penderson of Plymouth.

What is certain is the small group that started to gather around 5:30 p.m. soon grew to a few dozen, and then a few hundred people. By 6:30 p.m. Lower Circuit avenue was a sea of humanity. And most were only there because someone they never met said they heard from someone else the President was on his way.

“Look at all these people here,” said Johnny DeMarco of East Boston. “They must know something.”

But among the ranks of steadfast believers there were pockets of doubters. One man wearing a New York Yankees cap proclaimed the whole thing to be a big hoax. “Wouldn’t there be sharpshooters everywhere? Would they let all these people crowd around like this?” he wondered aloud.

“There is no emergency access, the sight lines are bad, and the roads aren’t blocked off,” said a doubting photographer for the Associated Press news service.

As for the Deon’s employees, they weren’t talking, although several waiters stood in the front window craning their necks to catch a glimpse of the President. Meanwhile, second-story decks and rooftops suddenly became prime real estate, as national media photographers negotiated with property owners to get a spot up in the air.

Down along Circuit avenue, which by now bore a close resemblance to Bourbon street during Mardi Gras, the excitement was palpable. One young girl exclaimed: “If I see him, I am going to die. I swear to God.”

After an hour, people were so desperate to see the President, they started to applaud anything out of the ordinary that came down the street. A Comcast van was a big hit with the crowd, and a female pedicab driver drew thunderous applause and cat calls.

The Oak Bluffs police arrived just at 7 p.m. to put up a barricade at the end of Circuit avenue. At 7:20 p.m. the first Secret Service arrived on the scene, their telltale ear pieces and matching polo shirts giving away their covert occupation. “Those are agents . . . we have agents,” declared the Associated Press photographer. “Maybe this is happening after all.”

At 7:24 p.m. all traffic was stopped, ratcheting the tension up another notch. “This is it . . . he’s coming,” shouted a young girl as her father hoisted her up onto his shoulders for a better view. Two minutes later, a caravan of black Chevy Suburbans appeared at the intersection of Pequot and Circuit avenues, not far from the entrance to Bangkok Thai.

“That’s her . . . that’s Michelle!” someone shouted. “White dress! White dress!”

“I think I see him! I think I see him! That’s him right there!” one man said.

Alas, this would be as close as most people would get to the President this evening; shortly after he exited the Suburban he quickly ducked not into Deon’s, but instead into the Sweet Life Cafe, leaving the throngs of onlookers and well-wishers heartbroken 100 yards down the road.

As the deflated crowd reluctantly began to disperse, a waiter from Deon’s came outside and announced: “We’re open for business.”

One man blamed no one in particular for spending two hours standing on the sidewalk with nothing to show for it.

“I knew we shouldn’t have believed it,” he said. “We could have eaten dinner already.”