Gary J. Byrne has devoted his life, and risked it, to serve his country — as a member of the US Air Force, a uniformed White House Secret Service officer, and a federal air marshal.

And he believes it is his patriotic duty to do anything he can to prevent Hillary Clinton from becoming president of the United States.

As someone who guarded the Oval Office during the Clinton presidency, Byrne, in an exclusive interview with The Post, tells how he witnessed “the Clinton machine leaving a wake of destruction in just about everything they do.”

He says he has also seen Hillary’s “dangerous,” abusive, paranoid behavior.

“It’s like hitting yourself with a hammer every day,” says Byrne, pounding a fist into his open hand, of the former First Lady’s explosive anger.

In his new book, “Crisis of Character: A White House Secret Service Officer Discloses His Firsthand Experience with Hillary, Bill, and How They Operate,” out Tuesday, Byrne makes no apologies for his anti-Clinton motivations.

“ ‘America first’ is in my blood,” he writes, sounding very similar to another presidential hopeful.

Byrne says he wants Americans to “vote [their] conscience,” but pledges to make sure “they have all the information that they need.”

For one, he thinks the Clintons’ own behavior bred an immoral White House culture.

Byrne revealed to The Post during the interview that Clinton staffers used cocaine on the job.

“There were some drug issues,” Byrne says. “Some people would come in to work in the morning, and they were barely walking, they would drop stuff off at the office, and go to the restroom where they would come out minutes later happy as a clown.”

He also exposes the “jogging list” for the first time.

“In the beginning of his first administration, when President Clinton was jogging outside, women who were dressed as if they were going clubbing or working out, started showing up at the southeast gate,” Byrne explains. “The agents . . . would get the women’s names, and run them to see who they were. If the women wouldn’t cooperate, they would be ushered out of the jogging group.

“Agents … insinuated that this list was used by President Clinton to try to meet these women,” Byrne says.

The book details how the president had as many as three mistresses during the same time period, including former Vice President Walter Mondale’s daughter, Eleanor, who Byrne once discovered “making out on the Map Room table” with Bill Clinton.

What bothered Byrne more than the infidelity was the way Bill Clinton programmed the entire White House to accommodate his cheating ways.

Hillary, meanwhile, was a human minefield. The Secret Service was convinced Hillary posed a physical threat to her husband, and even gave him a black eye, Byrne writes.

She also cursed out her security detail, and she and Bill would often try to evade the Secret Service, making it difficult to protect them and putting agents at greater risk, Byrne says. Bill and Hillary Clinton in 1999.Photo: Getty Images

But what sticks most in Byrne’s mind is the personal destruction the Clintons wrought in his own life – the fear and turmoil he had to endure as authorities subpoenaed and harassed him as they investigated the Monica Lewinsky scandal.

It all could have been avoided, Byrne maintains, if Bill Clinton had simply told the truth.

Byrne’s revelations have come under fire recently, with some critics doubting he had the access to the Clintons he claims he had, and that his book details do not align exactly with his testimony to prosecutors nearly two decades ago.

Hillary Clinton’s spokesman has ripped the book, telling Page Six “Gary Byrne joins the ranks of Ed Klein and other ‘authors’ in this latest in a long line of books attempting to cash in on the election cycle with their nonsense. It should be put in the fantasy section of the book store.”

“I know what the public image of the Clintons is and I know what the real image is. And the real one’s dangerous.” - Former Secret Service agent Gary Byrne

“Anybody who asserts that what I’m saying is not true,” Byrne says, his voice cracking with emotion, “they don’t know any better or they’re flat-out lying.”

Yet, he confesses, “I’m not completely comfortable telling the story, but I am telling it.”

He says a number of people could vouch for his access, including George Stephanopoulos, the former Bill Clinton communications director; John Podesta, Hillary’s campaign chairman, who worked in the Clinton White House; and Jennifer Palmieri, Hillary Clinton’s current campaign communications director, who worked near Byrne in the White House.

As for his testimony during the Ken Starr investigation, Byrne — who never signed a non-disclosure agreement with the Secret Service — says at the time he gave narrow answers to specific questions, as instructed.

“[I]f my testimony wasn’t true, I would end up doing seven years,” he says.

To prove he’s being truthful, he says, he’s willing to undergo a polygraph test — if Hillary takes one too.

Byrne says he is not committed to Donald Trump, despite sharing his slogans.

“The only thing I’ve ever heard about Donald Trump,” says Byrne, “was that he built a lot of buildings and he gave a lot of money away to charity.”

But, he says, he will never vote for a Clinton.

“I know what the public image of the Clintons is and I know what the real image is,” he says. “And the real one’s dangerous.”