(CNN) On the 75th anniversary of a defining battle of the defining war of human history so far, it's clear that military service has never been less important to American voters.

Six US presidents served overseas during World War II, but none since President George H.W. Bush have gone abroad, if they served at all. At this point, we might get a President who served in Afghanistan or Iraq -- that's South Bend Mayor Pete Buttigieg, Hawaii Rep. Tulsi Gabbard or Massachusetts Rep. Seth Moulton -- but it's almost certain the US will never have a commander in chief who served in Vietnam.

It has had three, including Trump, who found a way around the draft. That's old news, but it doesn't mean Trump won't still have to answer questions about it, as he did in Wednesday's interview with the British journalist Piers Morgan, who asked him if he would have liked to have served.

Trump "was never a fan" of Vietnam

The interview was conducted in the underground bunker where Winston Churchill led the British government during the Blitz and World War II.

"Do you wish you'd been able to serve? Would you have liked to serve your country?" Morgan asked.

Trump replied by questioning Vietnam, mirroring some of the anti-war sentiment of the '60s and '70s.

"Well I was never a fan of that war. I'll be honest with you. I thought it was a terrible war. I thought it was very far away. Nobody ever -- you're talking about Vietnam at that time and nobody ever heard of the country," Trump said, adding the non sequitur that, today, the government of Vietnam has been successful negotiating in global trade.

He went on to say that he wasn't active in protesting the war as a young man, but he didn't think the US should ever have taken part.

"But, uh, nobody heard of Vietnam and then say well what are we doing. So many people dying. So I was never a fan of -- this isn't like I'm fighting against Nazi Germany. I'm fighting -- we're fighting against Hitler. And I was like a lot of people. Now I wasn't out in the streets marching. I wasn't saying, you know, I'm going to move to Canada, which a lot of people did. But no, I was not a fan of that war. That war was not something that we should have been involved in."

Senator calls Trump a coward

Trump's comments drew a stinging rebuke from Sen. Tammy Duckworth, the Illinois Democrat and veteran who lost her legs in a helicopter accident while deployed to Iraq.

Appearing on CNN's "Anderson Cooper 360" Wednesday night, she called Trump a coward.

"I don't know anyone who has served in uniform, especially in combat, who would say they are a fan of war," she said. "In fact, I opposed the Iraq war, but volunteered to go when my unit was deployed."

JUST WATCHED Duckworth: Yes, I'm calling the President a coward Replay More Videos ... MUST WATCH Duckworth: Yes, I'm calling the President a coward 01:39

She accused him of using wealth and privilege to avoid service.

#CadetBoneSpurs: no one cares whether you were a "fan" of the Vietnam War. No one believes you were medically unfit to serve. You used your wealth & privilege to avoid serving your country five times, forcing another American to serve in your place each time. 1/ https://t.co/bSZbQlnWMf — Tammy Duckworth (@SenDuckworth) June 5, 2019

Making up for lack of service with spending

Trump said he's making up for his lack of military service by being President.

"Would you have liked to have served generally - perhaps in another (way)?" Morgan asked.

"I would not have minded that at all. I would have been honored. But I think I make up for it now. I mean look, $700 billion I gave last year and then this year $716 billion and I think I'm making up for it rapidly because we are rebuilding our military at a level that it's never seen before."

This deserves a quick fact check. Trump did not personally give the military $700 billion or $716 billion. Congress did, when it passed appropriations bills last year. Trump signed them, and it is his administration's responsibility to now spend the money.

But it says something about how he views his role as President and the dismissive way he's treated Congress and its responsibilities, that he takes personal credit for spending taxpayer money.

It's also more than a bit awkward for him to argue that the military will be built up to a level it's never seen before under him when he's preparing to commemorate D-Day, when the entire country was mobilized in the war effort. More than 16 million Americans served in World War II from a US population of around 140 million in 1940. It was a total war, even for the US, which was far from any of the front lines.

Fewer Americans serve

JUST WATCHED D-Day soldiers return to Normandy 75 years later Replay More Videos ... MUST WATCH D-Day soldiers return to Normandy 75 years later 02:53

The portion of the population that served in World War II is much larger than the portion that served during Vietnam, when more than 8.7 million Americans were in the military from a population of 203 million in 1970.

Despite the conflict in Afghanistan lasting longer than any in US history, fewer and fewer Americans have served in the military. The VA does not list a total number of service members during the wars in Iraq and Afghanistan, but there are currently about 1.3 million people in the military, coming from a population of close to 341 million, according to Census projections

6 Presidents served overseas in World War II

In the years after World War II, military service was almost a prerequisite for politicians and presidents for generations during and after World War II. Dwight Eisenhower, who was Supreme Allied Commander during World War II and gave the order for D-Day 75 years ago, went on to serve two terms as President. He ended hostilities in the Korean War shortly after taking office.

No more.

No presidents with Vietnam service

JUST WATCHED Vietnam veteran demands Trump show his bone spurs Replay More Videos ... MUST WATCH Vietnam veteran demands Trump show his bone spurs 01:59

Three of the last four US presidents -- Bill Clinton, Barack Obama and Trump -- had no military service at all. George W. Bush was a pilot in the Texas Air National Guard -- his way around Vietnam.

Two other politicians who were of military age during Vietnam are running against Trump as Democrats. They also deferred military service or sought to be exempt. All three are in their 70s, which makes it likely this is the last presidential election in which a Vietnam-era politician will be featured.

Sen. Bernie Sanders, the Vermont Independent who is running for President as a Democrat, applied to be a conscientious objector during Vietnam . The application was ultimately rejected, but he was too old to be drafted at that point. In 2015, he said during a CNN debate that he's no longer a pacifist.

JUST WATCHED Sanders: I opposed policy, not soldiers, in Vietnam (2015) Replay More Videos ... MUST WATCH Sanders: I opposed policy, not soldiers, in Vietnam (2015) 01:22

Joe Biden, the former vice president also running for President, received five Vietnam deferments for education and was later disqualified because of asthma

Two other politicians who came of age during Vietnam are running in the Democratic primary. Washington Gov. Jay Inslee received a student deferment and had a high draft number for his birth year, as did former Colorado Gov. John Hickenlooper

Plenty of Vietnam veterans have sought the White House, including medal of honor winner Bob Kerrey, who did not get very far. Several Vietnam veterans got their party's nomination, including Al Gore, John Kerry and John McCain.

Since the election of Bill Clinton over decorated former military pilot and wartime president George H.W. Bush in 1992, American voters have shown that avoiding service during Vietnam is not a dealbreaker.

A new generation of warrior politicians

A real question in 2020 is whether it's a desirable plus. There has been no draft since Vietnam, and there have been many fewer Americans serving in the military.

But there are multiple younger presidential aspirants who volunteered for the military and served in Iraq and Afghanistan.

Gabbard has made her military service a centerpiece of her campaign and cites it as the impetus for her platform of disentangling the US from foreign conflicts.

JUST WATCHED Moulton opens up about PTS: Extended interview Replay More Videos ... MUST WATCH Moulton opens up about PTS: Extended interview 11:32

Buttigieg also often cites his own volunteer service as an intelligence officer and his deployment to Afghanistan . He has criticized Trump for deferring military service during Vietnam.

Moulton served in Iraq as a Marine and has spoken publicly about the plight of veterans and his own struggle living with PTSD after coming home.