America wants to know: Who is the "mystery man" attached at Hillary Clinton's hip while she campaigns for the White House?

He's been on the stage, in her plane, by her side and following her everywhere she goes.

He touches her frequently, wrapping his arm around her or helping her up stairs, and responds immediately when Clinton has one of her coughing fits.

Some speculate he could be a physician on hand in case Clinton experiences a health emergency, a possibility considering nearly 71 percent of physicians informally surveyed by the Association of American Physicians and Surgeons said concerns about Clinton's health are "serious" and "could be disqualifying for the position of president of the U.S."

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The "mystery man" re-appeared Thursday in new video in which he's shown tailing the Democrat nominee, who is shielded from view as she exits her van:

In fact, the man has been apparently tailing the Clintons since at least January of 2013 – more than two years before Hillary announced her run for president. He was reportedly spotted in a vehicle with former President Bill Clinton three years ago, according to London's Daily Express. A photo caption said the two were leaving the New York Presbyterian Hospital after visiting Hillary, who was receiving treatment for a blood clot in her head that was discovered following a concussion.

As WND reported, after Clinton suffered the worst coughing fit of her campaign Monday, the "mystery man" suddenly appeared on her plane.

The following image of the man on the plane was posted by the Gateway Pundit blog:

In the past, the same man has been spotted helping Clinton climb stairs:

At an earlier campaign appearance, the same man was reportedly seen holding what some say appears to be a Diazepam pen – though others argue it actually resembles a mini flashlight.

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Radio host Tammy Bruce made an appearance Wednesday on Fox Business' "Varney & Co." in which she discussed Clinton's "mystery man."

"He actually moves other Secret Service agents off the stage," Bruce noted. "We have not been informed who he is so we have to guess, in some way, who he is. But he seems to be playing a very personal role. He appears when she seems to be in trouble, either with the coughing or with some health issue or ... in her own personal reaction to what was a heckler ... It's troubling because you've got a man who is also doing something that the Secret Service wouldn't do. He's very physical with her. He touches her. He has his arm around her. ... It's a legitimate question. Her health is legitimate."

Watch Tammy Bruce's comments:

But former Secret Service agent Dan Bongino, who protected President Barack Obama and is author of the New York Times bestseller "Life Inside The Bubble: Why A Top-Ranked Secret Service Agent Walked Away From It All," said he believes there's a simple explanation – and that explanation doesn't rule out serious health concerns surrounding Clinton.

Bongino told Fox Business on Thursday: "He's most likely a supervisory agent with the Secret Service who is what we would call kinda like a body man."

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In one campaign rally incident, protesters grew rowdy. The "mystery man" rushed the stage, put his hands on Clinton and then muttered to her, "Keep talking." Some have insisted that the "mystery man's" behavior was unlike that of a Secret Service agent.

"I'm not really sure why he said, 'Keep talking,'" Bongino said. "It seems kind of strange. That would be more of a staff function. But, as for responding to the stage when she's in what may have been some kind of a medical crisis, that's not really unusual at all. ... About 50 percent of what we (Secret Service agents) do is first respond to (inaudible) medical training, so I'm not really surprised that some of them would pounce on the stage if they thought something might be wrong medically.

"Although I bet the staff, given the implications of this, is probably telling him to back down a little bit. There's always friction with the staff on this stuff, because they don't want this out there that she has a medical problem."

Watch former Secret Service agent Dan Bongino's comments:

Bongino added, "I'm pretty sure he's just doing his job with the Secret Service. ... He's probably super uncomfortable right now with all this attention."

Secret Service agents are, in fact, trained in "emergency medicine," according to the agency's website.

Author Henry Holden explains in his book, "To Be A Secret Service Agent": "Johns Hopkins (medical) University liasons are at the Secret Service's Beltsville training location, where agents complete initial medical training and later recertification. Hopkins supports first-responder training for all personnel and advanced training (to the emergency medical technician or paramedic level) for selected agents."

The Washington Post's David Weigel identified the "mystery man" as Secret Service Assistant Special Agent in Charge Todd Madison.

WND's messages to both the Hillary Clinton campaign and the U.S. Secret Service inquiring about the man's identity hadn't been returned at the time of this report.

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