President Trump signs autographs as he greets Marines aboard the USS Wasp on Memorial Day . (Brendan Smialowski/AFP/Getty Images)

President Trump, who has touted himself as an unmatched ally of military veterans, is facing pointed new attacks from Democratic presidential candidates who question his medical deferment from service in Vietnam — and, in turn, his patriotism and integrity.

Leading the assault are two military veterans: South Bend, Ind., Mayor Pete Buttigieg and Rep. Seth Moulton (D-Mass.). They have offered searing assessments of Trump, accusing the president of faking a disability and forcing another American of Trump’s generation to risk his life in the jungles of Southeast Asia.

Trump, who had been traveling in Japan, has not yet responded to either Democrat, but he has long defended his deferments as legitimate. More broadly, he portrays himself as a vigorous friend to the military, pushing for a buildup of the armed forces, praising military leaders, reaching out to veterans and promising to avoid misguided wars.

But the questioning of the 1968 diagnosis of bone spurs in his heels presents a challenge for a commander in chief who has tapped generals for his Cabinet and asked the Pentagon to plan a parade celebrating the military. It could test whether the president’s political coalition, which includes many military families, can be cracked.

“I don’t think that lying to get out of serving your country is patriotic. It’s not like there was just some empty seat in Vietnam. Someone had to go in his place,” Moulton said Sunday on MSNBC. “I’d like to meet the American hero who went in Donald Trump’s place to Vietnam. I hope he’s still alive.”

Buttigieg, speaking at a Washington Post Live event last week, said of Trump, “This is somebody who, I think it’s fairly obvious to most of us, took advantage of the fact that he was a child of a multimillionaire in order to pretend to be disabled so that somebody could go to war in his place.”

Buttigieg, 37, then made an overture to Republicans to reconsider their support of Trump, saying he was “old enough to remember when conservatives talked about character as something that mattered in the presidency.”

The flap could propel Democrats toward a more direct discussion of matters of war and service as the 2020 campaign intensifies. Following victories by several Democratic veterans during the 2018 elections, party leaders are putting an emphasis on the protection of diplomatic and military norms amid Trump’s shattering of them.

“This isn’t the usual playbook against a Republican, but they’re not doing it as a playbook,” said Democratic strategist Robert Shrum, who was a top adviser on Vietnam veteran John F. Kerry’s 2004 presidential campaign. “It’s part of the flow of conversation about this president on his patriotism and truthfulness, and a sign of how they’re not going to let him push them around.”

Still, Kerry’s experience could provide a cautionary tale about the political power of military service. Kerry, a former senator from Massachusetts, was a war hero wounded in Vietnam, but that did not prevent unsubstantiated attacks on his record that resonated with some conservatives.

The critiques mark the first time that Trump has been confronted so directly on allegations of draft-dodging. His 2016 rivals of both parties rarely broached the topic, even after he assailed John McCain, the late senator and Republican presidential nominee who was a prisoner of war in Vietnam for over five years.

In a crowded Democratic presidential field, Buttigieg and Moulton, along with Rep. Tulsi Gabbard (D-Hawaii), regularly cite their time in uniform as they look to stand apart from competitors.

“I don’t have a problem standing up to somebody who was working on Season 7 of ‘Celebrity Apprentice’ when I was packing my bags for Afghanistan,” Butti­gieg said Thursday during his Post appearance.

Buttigieg was commissioned as an intelligence officer in the Navy Reserve in 2009 and was deployed to Afghanistan in 2013, while serving as mayor. Gabbard, 38, served in a field medical unit of the Hawaii Army National Guard in a combat zone in Iraq from 2004 to 2005 and was deployed to Kuwait from 2008 to 2009. Moulton, 40, served as a Marine Corps captain in Iraq and was an aide to Gen. David H. Petraeus, then the U.S. commander in Iraq.

Although Gabbard has not engaged Trump’s lack of military service in the same way as Buttigieg or Moulton, she has suggested Trump does not understand the human cost of war and is susceptible to pursuing “stupid wars” in places such as Iran because he has hired hawkish advisers such as national security adviser John Bolton.

“If the main way our President creates a strong economy is to sell weapons to Saudis to bomb innocent people in countries like Yemen, then we need a new president,” Gabbard tweeted heading into Memorial Day weekend.

Other Democratic presidential candidates are grappling with the complicated legacy of Vietnam in different ways, from touting their antiwar activism to showing solidarity with Vietnam veterans.

“As a young man, along with Dr. Martin Luther King Jr. and others, I marched against the war in Vietnam,” Sen. Bernie Sanders (I-Vt.), who applied for conscientious objector status in the 1960s, said Saturday at a rally in Burlington, Vt.

Sanders, who speaks proudly of his time as chairman of the Senate Veterans’ Affairs Committee, added that Vietnam “ravaged my generation, which left 59,000 brave young Americans dead, as well as killing over a million Vietnamese people. I make no apologies for having opposed that war.”

Former vice president Joe Biden, for his part, received four deferments during the 1960s when he was in college and at law school, and then received a fifth and final medical-related deferment in 1968. Like Trump, Biden’s status was “1-Y,” or unqualified for duty except in a national emergency, in his case due to asthma.

Unlike Sanders, Biden did not closely associate with the antiwar movement. “I’m not big on flak jackets and tie-dyed shirts,” Biden said in 1987, during his first bid for the White House.

Presidential historian Douglas Brinkley said the Vietnam War carries an emotional wallop more than four decades later.

“Vietnam is still with us,” Brinkley said. “It was a defining, seminal moment, and older voters especially are curious about whether you were a hawk or a dove, or how you dealt with Vietnam when our country was divided.”

Those who served have a better case to criticize their political opponents, he said. “If you put your head down, like Biden, it’s hard to score points,” Brinkley said.“But if you’re younger and served, Trump is seen as vulnerable.”

The Associated Press’s VoteCast poll of midterm voters last year found that 56 percent of veterans approved of Trump’s performance as president, while 43 percent disapproved — a stronger approval rating than among nonveterans.

Debates over military service in Vietnam have featured in previous presidential campaigns, most notably in 1992, when Bill Clinton, whose campaign was under scrutiny on this front, revealed a letter in which he thanked a military recruiter “for saving me from the draft” during Vietnam.

During the 2000 campaign, George W. Bush faced questions about his time in the Texas Air National Guard. Bush maintained that he joined the unit not to avoid service in Vietnam but because he wanted to be a fighter pilot.

Trump, after graduating in 1964 from the New York Military Academy, where he played football and basketball, obtained four separate deferments so he could study at Fordham University and the University of Pennsylvania. Then, in September 1968, he was medically disqualified, according to the ledger from his local Selective Service System draft board in Jamaica, N.Y., which is in the custody of the National Archives.

The ledger does not detail why Trump failed the exam, and the Selective Service destroyed all medical records and individual files after the draft ended in 1973.

The New York Times reported last year that the daughters of a deceased podiatrist said it was “family lore” that their father, as a “favor,” provided the fall 1968 diagnosis and, in return, received access to Fred Trump, Trump’s father and owner of the Queens building in which the father practiced.

Trump obtained his medical deferment as the Vietnam War was escalating and the military needed a wave of new conscripts. In some interviews, Trump has cited his medical deferment. In others, he has said he simply lucked out in the 1969 lottery.

“I had a lot of deferments. I had a foot deferment for a short time. And then I got a lucky number. I got 356 over 360 or something. You don’t get a luckier number than that,” Trump said in an interview with The Post in December 2015.

At the time, young men with the same birth date as Trump — June 14 — were assigned draft number 356 out of 366. Anyone with that number was almost guaranteed to avoid being drafted, unless the entire country mobilized.

Trump said in the 2015 interview, “I’ve always felt somewhat guilty about because I didn’t serve like many other people.”

Trump recalled that he donated $1 million of the $2.5 million needed to fund a memorial to Vietnam veterans in New York in 1985, a donation that was documented by New York news outlets at the time.

“What I did to make up for my guilt is I built the Vietnam memorial,” Trump said. “I spent a fortune, by the way. I built the Vietnam memorial in downtown Manhattan. To this day, people love it. They come up and they thank me.”

Craig Whitlock, Amy B Wang, and Felicia Sonmez contributed to this report.