Editor's note: This story has been updated to remove the assertion that the Secret Service may have broken protocol in responding to Clinton's illness, which was published before the agency was able to respond. In a statement sent later, a spokesman for the agency said that "at no time did any Secret Service personnel violate security protocols."
The U.S. Secret Service followed atypical protocol with Hillary Clinton's early departure from Sunday's commemoration of the 15th anniversary of the 9/11 terrorist attacks at Ground Zero.
In a widely circulated video of the Democratic presidential nominee's departure from the ceremony, Clinton can be seen leaning against a security bollard and then buckling and stumbling as her security detail helps her into a black van. Clinton's campaign said she had suffered from overheating.
According to two former Secret Service agents who reviewed the video, the detail clearly had to rush and did not expect Clinton to leave at that time. They said the Service generally prefers for the protected individual not to wait for a car to arrive, although that has happened before. In the video, Clinton is leaning against the bollard as a black van pulls up.
One former agent said the risk of waiting was diminished considerably on Sunday by the thick bubble of security surrounding the commemoration. Protective details for Homeland Security Secretary Jeh Johnson, Republican presidential nominee Donald Trump and other city officials were also on hand.
It is also unusual for a detail leader to leave the protected individual's side, as a Secret Service agent, Todd Madison, is seen doing in the video, to open the van's doors. Opening the van is typically left to another agent. But because of the rushed nature of the departure, one of the former agents said, another rule of Secret Service protection appears to have carried the day: Whoever is closest to the door must open it.
“Every once in a while, you have to call an audible,” one of the former agents said. “We follow a methodology, not a script.”
The video also shows a dense thicket of agents closing around behind Clinton, giving her 360 degree coverage – another mainstay of Service protection.
Secret Service spokeswoman Cathy Milhoan issued the following statement later Sunday: "During the early departure today of one of our protectees, at no time did any Secret Service personnel violate security protocols."
Milhoan later added: "The Secret Service is confident in the actions taken by its Protective Detail earlier today."
The incident also raised questions about Clinton's traveling group of reporters, which she left behind at Ground Zero when she departed unexpectedly, leaving the press with no knowledge of her whereabouts or condition for about 90 minutes.
Clinton travels with a small group of reporters and photographers representing broadcast and print outlets. The arrangement, called a “pool,” approximates the rotating group of press outlets that travel with the president.
Trump has no such pool, a break with past candidates. He had no reporters with him Sunday, when he appeared unannounced at the same memorial ceremony Clinton attended.
Clinton resisted very close contact with her pool over the summer, consenting only to travel on her own small jet in tandem with the pool, and not allowing the same kind of full-time coverage customary at the White House.
Starting on Labor Day, Clinton began traveling on the same large campaign plane with her Secret Service detail and reporters, and the pool has had greater access to some of her events, including a fund-raising party in New York on Friday night that featured Barbra Streisand. At that event, Clinton stirred controversy by referring to some Trump supporters as “deplorables.”
In the White House model, a so-called protective pool is on constant standby each day until given an all-clear that the president will not have any further public events or outings. That model has been followed more closely by presidential candidates in the past.
Clinton is not allowing door-to-door pool coverage, in which the pool group would assemble at her home and travel with her from there. Instead, pool reporters have met up with Clinton at her plane or elsewhere. On Sunday, the pool was left behind both when Clinton departed the memorial and when she departed daughter Chelsea Clinton’s apartment. The pool was later driven separately to Westchester County, where the Democratic nominee lives.
Robert Gibbs, President Obama's first White House press secretary, suggested in a tweet Sunday that it's time for Clinton to adopt a more formal protective pool.
"Protective pool isn't always easy for either candidate or press but there comes a point for each nominee when it must be part of daily life," he said.
John Wagner contributed to this report.