U.S. Secret Service may have broken protocol while protecting Democratic presidential nominee Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE in New York City Sunday, The Washington Post reports.

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Clinton left a 9/11 memorial ceremony early after feeling ill, and can be seen in a widely circulated video standing by a curb with aides while waiting for a car to arrive. As she prepares to enter the car, she can be seen wobbling and needing help to remain standing.

The Washington Post reports that it is against Secret Service protocol for protected individuals to wait for their car to arrive.

It is also unusual for a detail leader to leave the protected individual's side, as agent Todd Madison appears to do in the video showing him stepping away to open the van's doors.

However, in a tweet Sunday evening the Secret Service said it had not violated protocol.

FACT CHECK: At no time did @SecretService personnel violate security protocols during the early departure of one of our protectees. — U.S. Secret Service (@SecretService) September 11, 2016

Clinton left the ceremony after feeling "overheated," aides said.

She rested for about 90 minutes at the apartment of her daughter Chelsea before emerging and telling reporters she felt great. She then returned to Chappaqua, N.Y., where she was examined by her doctor.

Dr. Lisa R. Bardack released a statement hours after the Democratic presidential nominee returned home, saying Clinton has been ill with pneumonia. She said the incident Sunday was a result of dehydration and overheating and that the candidate is "re-hydrated and recovering nicely."

Updated 5:42 p.m.