Clint Hill was the Secret Service agent who climbed onto the back of President John Kennedy’s limousine as gunshots rang out in Dallas in November 1963. (James W. Ike Altgens/AP)

Carol D. Leonnig, an investigative reporter at The Washington Post, won the Pulitzer Prize for her coverage of the Secret Service’s recent struggles and security failures in protecting the president.

When Clint Hill watches Hillary Clinton, Donald Trump or any presidential contenders verbally spar on television, he barely looks at the candidates or listens to the barbs they hurl. Hill, one of the heroes of the Secret Service, instead trains his gaze on the icy-faced special agents in suits on the edge of the screen and worries about the vitriol of this campaign season: It could happen in an instant. Somebody could get shot.

“Whenever I watch, I sit on the edge of my chair,” Hill said. “Yeah, it gives me pause every time.”

It’s an understandable reaction for an elite bodyguard who spent nearly two decades protecting America’s presidents and has seen political rhetoric turn ugly and divisive before. Hill carries a unique battle scar: He was a step or two away when an assassin’s bullet pierced President John F. Kennedy’s skull. A legend in the close-knit world of former and current Secret Service agents, Hill is perhaps best known as the lone agent who raced toward Kennedy’s limousine at the sound of gunshots during the 1963 motorcade in Dallas and hurled himself onto the trunk in a failed attempt to shield the young leader and his wife.

Hill, who has written books about the assassination and his time protecting first lady Jacqueline Kennedy, is back now with “Five Presidents: My Extraordinary Journey With Eisenhower, Kennedy, Johnson, Nixon and Ford.” Hill and his co-author, Lisa McCubbin, take readers from Hill’s hiring in 1958 and his work in the agency’s Denver field office to the shock of Kennedy’s death and the agent’s vigilance afterward to prevent such a disaster from happening again. It closes with Hill’s eventual realization that he is mentally and physically broken and must retire in 1975. After years of sustaining a breakneck work pace to numb the memory of losing Kennedy, he fell into heavy drinking, failed a physical and left the service at age 43. He found solace when he started to talk through, and eventually write about, what happened.

Hill was a Secret Service agent from 1958 to 1975. (Tom Pennington/Getty Images)

McCubbin said Hill went into each of his books begrudgingly, “not sure anyone would be interested.” But what he considered a mildly routine day at work, she said, would have been a lifetime memory for most Americans.

Adopted as a newborn, Hill was raised by a loving North Dakota couple. After graduating from college, serving in the Army intelligence corps and starting his own family, Hill applied on a whim for an open Secret Service position. He got the job. One of his first tasks was guarding the Denver home of President Dwight Eisenhower’s 80-year-old mother-in-law. Soon after, he was summoned to the White House detail to help shadow Eisenhower. That detail is still the most prized assignment in the service, putting an agent on the right or left flank of the president when he is in the midst of making history, meeting celebrities or staring down a national crisis.

Hill visited 11 countries with Eisenhower during a massive 1959 peace-building campaign, took a helicopter tour of Washington with President Lyndon Johnson to see the devastation from the riots after the Rev. Martin Luther King Jr.’s assassination, and stood on the South Lawn as a disgraced President Richard Nixon boarded Marine One for the last time and left the White House. He met Arnold Palmer when Eisenhower played golf with him at Augusta National, got the word that Elvis Presley had showed up unannounced at the White House’s northwest gate to talk to Nixon and was at Cape Canaveral to watch the Apollo 11 launch, which first put men on the moon.

Some of the most vivid, hair-raising moments in “Five Presidents” come as Hill recounts his frustration in trying to create a secure bubble around an uncooperative and unpredictable Johnson. By all rights, Johnson should have had plenty of motivation to play it safe and defer to the service about his personal security. He had gone from being Kennedy’s vice president on that trip to Dallas in November 1963 to hastily arranging his own swearing-in as president two hours later on the tarmac at Dallas’s Love Field. Johnson took the oath aboard Air Force One as the late president lay in a casket in the aft cabin and his shocked widow stood witness in a bloodied pink suit.

Hill was assigned to continue as the lead agent protecting the former first lady for a year, then worked on Johnson’s detail. Hill found he wasn’t too keen on the hot-tempered and sometimes crude president after spending nearly four years with the refined, soft-spoken Jackie Kennedy. Johnson almost booted Hill off the team the first night he arrived for duty at his ranch near Austin, after Johnson recognized him on the grounds. The president privately questioned Hill’s loyalty since he had been so close to the Kennedys. Gradually, though, Hill won Johnson’s respect, to the point where the president agreed that Hill should become the agent in charge of his detail. Nevertheless, Johnson was a nettlesome client, always jumping out of his limo to shake hands and surprising his agents with snap decisions to travel somewhere without any notice.

That included helicoptering over to a neighbor’s ranch for an impromptu drop-in, as well as a stunning December 1967 around-the-world journey that started as a visit to Melbourne for the funeral of Australia’s prime minister. Johnson surprised the service, most of his staff and the press by telling them after the funeral that he wanted to pop in on the pope and then visit U.S. troops in Thailand and the Cam Ranh Bay Air Base in Vietnam. Hill felt a mixture of pique and dread, he recalled: “Here I was,” the agent in charge of Johnson’s safety, “headed into a combat zone, and I had no idea what the man was going to do next.”

After Johnson left office, Hill oversaw the details for Nixon’s two vice presidents and eventually became an assistant director of the service. In 1973, as the Watergate investigation heated up, Hill was asked to interview for the job of the departing director. But he took himself out of the running, telling Treasury Secretary George Shultz that he was too emotionally and physically battered for the role. Two years later, Hill’s doctor told him he had to get away from the service if he wanted to live to a healthy old age. He took the advice. Now 84, he lives on the West Coast.

(Gallery)

The business of protecting the president has changed dramatically since Hill’s days, especially in the size of the teams and the technological tools they deploy. The Secret Service has 10 times as many agents as it did when Hill joined, and he fears that agents have lost a sense of brotherhood as the agency has grown. Hill says one struggle that still plagues the service after all these years: getting the White House and Congress to give it enough staff and money to provide the safest environment for those who get protection.

“They’re straining at the seams” to cover the presidential candidates today, Hill said. He argues that agents — not the officials who control the purse — will be blamed if something terrible happens. The service has in recent years “asked for additional manpower and it’s been denied by Congress. When there’s a problem and it’s evident the problem is caused by the lack of manpower, Congress is not going to take the blame but instead, it is going to point the finger.”

Twitter: @CarolLeonnig

Five Presidents
My Extraordinary Journey With Eisenhower, Kennedy, Johnson, Nixon, and Ford

By Clint Hill with Lisa McCubbin

Gallery. 345 pp. $28