Two veterans of the Iraq and Afghanistan wars seeking the 2020 Democratic presidential nomination have taken aim at President Trump over his four Vietnam draft deferments for being a student and a medical one in 1968 for a bone spur.

But their ultimate target might be Joe Biden, the early Democratic front-runner who avoided Vietnam service in a strikingly similar way by securing five student deferments and a medical one in 1968 due to childhood asthma.

“I have a hard time believing any major candidates will attack Biden directly on the issue,” Democratic strategist Brad Bannon told the Washington Examiner, “but they could be trying to raise it subliminally.”

Pete Buttigieg, the mayor of South Bend, Ind., and a Navy veteran of Afghanistan, last week accused Trump of draft dodging. "I have a pretty dim view of his decision to use his privileged status to fake a disability in order to avoid serving in Vietnam," he said.

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Seth Moulton, a Massachusetts representative and a former Marine officer who served in Iraq, blasted Trump on the same grounds. "This is a president who used his father's connections to lie about bone spurs to get out of serving in a war," he said this month. Moulton revealed this week that has post-traumatic stress disorder as a result of his combat experience.

After his four education draft deferments, Trump received a 1-Y medical classification in 1968 when he received a diagnosis of bone spurs in his heels. The daughters of the now-deceased podiatrist who made the diagnosis allege the diagnosis was a favor to Fred Trump, the president’s father. Former Trump lawyer and fixer Michael Cohen said in February that Trump told him, "You think I'm stupid, I wasn't going to Vietnam," and that there were no medical records relating to the bone spur.

Biden also received a 1-Y classification in 1968, meaning that he was unqualified for duty except in a national emergency. He was " disqualified from service because of asthma as a teenager," according to Barack Obama's 2008 campaign.

Despite his childhood asthma, Biden recounted an active youth in his 2007 book Promises to Keep. He worked as a lifeguard, mentioned playing basketball, and was on his high school football team. "I'd never in my life had any real physical troubles beyond childhood asthma or a separated shoulder," Biden wrote.

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Joe Trippi, a veteran Democratic strategist, said he saw the attacks on Trump as a "legitimate way for veterans like Buttigieg and Moulton to contrast their life experience with Biden and others in the race."

Republican strategist Ford O’Connell predicted Democrats would start to attack Biden more explicitly, but to do so in a way that did not undermine the Obama administration's record. The Vietnam issue “is a good issue to go after him on because in no way does it implicate Obama,” he said, noting Obama’s high approval among the Democratic electorate.

Biden told the Washington Post in 1987, during his first presidential run, that other people "felt more strongly than I did about the immorality" of the Vietnam War. "My view of it was it didn't make sense. It was lousy policy," adding that he was "prepared" but not "anxious" to go to Vietnam. At another point in 1987 Biden said in reference to anti-war protesters: "I'm not big on flak jackets and tie-dye shirts."

In later life, Biden gained a connection with the military through his son Beau, who died of brain cancer in 2015 at age 46. He was in the Delaware Army National Guard and was deployed to Afghanistan for a year. Biden's other son, Hunter Biden, now 49, joined the Navy in 2014 but was discharged after testing positive for cocaine.

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Scrutiny over lack of Vietnam service has long haunted politicians. In 2004, Democratic presidential candidate and then-Sen. John Kerry, a decorated Vietnam veteran, said that Vice President Dick Cheney ''got every deferment in the world and decided he had better things to do.'' Cheney received four student deferments and one for being a new father.

Candidate Bill Clinton came under fire in 1992 for enrolling in, but not joining, the ROTC as a way to avoid the draft. Clinton thanked his ROTC recruiter in a letter for "saving me from the draft."

President George W. Bush joined the Texas Air National Guard days before his student draft deferment expired, allowing him to fulfill his service in Texas rather than Vietnam. Though there was normally a long waiting list to join and he scored the lowest acceptable grade on his pilot aptitude test, Bush, whose father was a congressman at the time, was sworn in the same day he applied.