Correction: An earlier version of this story cited Abraham H. Foxman, national director of the Anti-Defamation League, as saying that Hagel’s position on Israel “borders on anti-Semitism.” Foxman was referring specifically to Hagel’s use of the expression “Jewish lobby” in comments he made for a 2008 book, not to his position on Israel broadly.

Shards from a Viet Cong mine are still embedded in Chuck Hagel’s chest, 44 years after his infantry squad walked into a booby trap in the Vietnam jungle. Scar tissue marks the left side of his face from another mine explosion, barely a month after his first brush with death.

“I remember,” Hagel told an interviewer for the Library of Congress’s Veterans History Project in 2002, “thinking to myself, you know, if I ever get out of all of this, I am going to do everything I can to assure that war is the last resort that we, a nation, a people, calls upon to settle a dispute. The horror of it, the pain of it, the suffering of it. People just don’t understand it unless they’ve been through it.”

Today, Hagel, 66, heads President Obama’s shortlist of candidates to lead the Pentagon. If he is nominated by the White House and confirmed by the Senate, he would become the first defense secretary with a Purple Heart, the combat decoration for those wounded in battle, since Elliot L. Richardson, who held the job briefly during the Nixon administration.

Hagel served 24 months in the Army as an enlisted grunt before embarking on successful careers in business and politics that saw him earn millions and win election to the Senate, twice, as a Republican from Nebraska.

Although his views on whether the Vietnam War was justified have changed over time, Hagel’s combat experiences have consistently driven his approach to foreign policy, his political passion.

As a senator, he voted to authorize the war in Iraq but soon became the most vocal and cutting Republican critic of the George W. Bush administration, accusing it of bungling the occupation. In 2007, he warned that Bush’s plan to send 30,000 more troops to Iraq would be “the most dangerous foreign policy blunder in this country since Vietnam, if it’s carried out.”

His unbridled assessments left other Republicans wondering whose side he was on and thoroughly alienated the GOP’s neoconservative wing, which still hasn’t gotten over its resentment. In recent days, some of them have intensified a campaign to shoot down his potential nomination even before Obama has made an announcement, ripping Hagel for what they consider his weak stance on Iran and his insufficient support of Israel.

“Stopping a war is a hell of a lot harder than starting it, and Chuck understands that,” said Bob Kerrey, another former Nebraska senator and Vietnam War hero. “Sometimes it provokes cries from the right that he’s soft. But it’s just that he’s experienced it, and it animates him.”

At times, however, Hagel has almost seemed to delight in thumbing his nose at his party. During this fall’s campaign, signs supporting Obama and Democratic candidate for Senate Timothy M. Kaine were posted on the front yard of his Northern Virginia home. Hagel said his wife, Lilibet, put them up, but he didn’t disavow them, either.

Four days before the election, he further irritated the GOP by publicly endorsing Kerrey, a Democrat, making an ultimately futile bid to reclaim an open Nebraska Senate seat, even though Hagel had previously said he wouldn’t take sides in the race. Hagel said he acted in an attempt to help break the partisan “nonsense that’s literally strangling our country.”

Hagel declined to be interviewed for this article. But in recent years, he has repeatedly complained that he no longer feels comfortable in the GOP.

“I think the case could be made that I am the true Republican and that the party came loose of its moorings,” he told the Lincoln, Neb., Journal Star days before he left the Senate in January 2009. “I’ve heard so many times from Republicans that, ‘You’re right, but why do you have to say it?’ And I say: ‘I’m going to tell you what I think.’ ”

Like another blunt-spoken Vietnam veteran — Sen. John McCain (R-Ariz.) — Hagel styles himself as an independent thinker. Whether that has helped or hindered his political career is an open question.

After toying with the idea of running for president in 2008, first as a Republican and then as an independent, Hagel decided instead to retire from the Senate and leave politics. Disaffected Republicans in Nebraska said he was scared of a primary challenge.

“There was just so much disdain for Senator Hagel. It wasn’t so much his policy positions as the way he conducted himself, appearing on every Sunday talk show, attacking President Bush day in and day out,” said Mark Fahleson, the Republican Party chairman in Nebraska. “It wasn’t the Nebraska way. He did burn a lot of bridges at the end.”

That may help explain why some Bush supporters, neoconservative commentators and pro-Israel groups have fueled a vigorous public lobbying effort to deter the Obama administration from nominating him.

As a senator, Hagel angered those factions by voting against some sanctions against Iran and by trying to undercut their arguments about the need to consider military action against Tehran to prevent it from going nuclear. In addition, Hagel has signaled a willingness to negotiate with the Iranians and the Palestinian Hamas movement, despite their hostility toward Israel.

Some of Hagel’s opponents have gone further by implying that he is anti-Semitic. They cite a comment he made in an interview for a book published in 2008, when he said: “The Jewish lobby intimidates a lot of people up here.”

Abraham H. Foxman, national director of the Anti-Defamation League, said he does not believe Hagel is an anti-Semite — “absolutely not,” he said — but added that he believes the former senator’s use of the expression “Jewish lobby” “borders on anti-Semitism.”

“We’re not going on a campaign. We’re not against him,” Foxman said in a telephone call from Israel, where he was traveling. “But his appointment would be of concern and troubling to the community.”

Hagel’s supporters say his critics are misrepresenting his positions. Any suggestion that the former senator is anti-Semitic is “crossing a line,” said Jeremy Ben-Ami, executive director of J Street, a liberal pro-Israel group.

“We’re tremendously supportive. We find him to be a true expert and a real guiding light on national security,” Ben-Ami said. “We’re frankly very disturbed to watch some of the attempts going on to disqualify him. Throwing around charges of anti-Semitism so lightly really dilutes the term to the point it becomes meaningless.”

A military upbringing

Hagel was born in North Platte, Neb., in 1946. His parents married shortly after his father, Charles, returned from the Pacific theater, where he served in the Navy during World War II.

Chuck was the eldest of four children, all boys. The family was poor and moved from small town to small town across Nebraska because their father had trouble holding a job. Charles Hagel was a hard drinker and sometimes physically abusive, traits that his sons later came to associate with post-traumatic stress from the war. He died at age 39 of a heart attack, leaving 16-year-old Chuck as the man of the family.

Five years later, Chuck Hagel enlisted in the Army. He was sent to Vietnam, where he served in the 9th Infantry Division.

His brother Tom, two years younger, joined up soon after. Unusually, the brothers were assigned to the same squad. The first time Chuck was struck by shrapnel, Tom stopped the bleeding and saved his life. During a second mine attack a month later, the roles were reversed and Chuck rescued Tom, who was knocked unconscious in the explosion.

After they came home from the front, the brothers argued violently over the meaning of Vietnam. Chuck saw it as a righteous cause. Tom, disillusioned, became a vocal opponent of the war and a liberal Democrat. Fistfights failed to settle their differences.

Over time, however, the future senator changed his mind. He has said the final straw came with the release of taped conversations in which President Lyndon B. Johnson acknowledged that the war was unwinnable but that he would send more troops to Vietnam anyway.

Clashes with GOP

Hagel first came to Washington in the 1970s as a GOP congressional staffer. In 1981, President Ronald Reagan appointed him as deputy administrator of the Veterans Administration. But he quit after clashing with his boss, Robert Nimmo, who curtailed veterans’ benefits and compared the side effects of exposure to Agent Orange to “a little teenage acne.”

With his political options limited, Hagel entered the business world and hit the jackpot, helping to start a telecommunications firm that specialized in a new technology: cellphones.

In 1996, Hagel returned to Washington as Nebraska’s first Republican senator in a ­quarter-century. He was reelected six years later with 83 percent of the vote and was a rising star in the GOP. That began to change after the invasion of Iraq.

Hagel’s relentless criticisms of the Bush administration — especially Vice President Richard B. Cheney and Defense Secretary Donald H. Rumsfeld — isolated him within the party, even as Democrats warmed to him.

“I remember him telling me how uncomfortable it was for him to go to Republican caucus meetings, especially when Cheney was there,” said Ross K. Baker, a political science professor at Rutgers University who served on Hagel’s staff as an academic observer while conducting research. “Hagel would go, and Cheney would sort of give him the hairy eyeball.”

But the hostility from the White House and the party leadership failed to mute Hagel. “The Vietnam experience, I think, gave him the boldness to speak independently,” Baker said. “It’s kind of hard to intimidate a combat veteran by threatening to withdraw a committee assignment.”

Hagel remains personally close to many of his former colleagues in the Senate. But some GOP senators have signaled that they are concerned about the objections by pro-Israel groups, raising the possibility that Hagel might face stiffer questioning from Republicans than Democrats if nominated.

Sen. Richard G. Lugar (R-Ind.), a foreign policy mentor to Hagel who is leaving the Senate after losing his reelection bid in a primary, called the Nebraskan “an excellent candidate.” But he stopped short of saying that Hagel would sail to confirmation.

“Most senators who served with Chuck would be favorable to his nomination,” Lugar said, before noting that the chamber has changed in makeup since Hagel left four years ago.

Might his nomination run into trouble? “I would hope not, but I have no way of knowing in advance,” Lugar said.