When I came back from Iraq the second time, I had trouble driving. My tours as a Marine had shown me how easily metal could tear through flesh. Now I was acutely aware that life is precarious. I was amazed that people could be blasé while driving 80 mph. Could they not see that a small mistake could be enough to kill them?

I feel the same way now as an American citizen, watching a good portion of the country consider voting for Donald Trump. Having grown up in the Midwest and served in the military, I can understand why both have large constituencies supporting the Republican presidential candidate. But I believe Trump supporters underestimate how fragile what we have is.

I can appreciate the frustrations of Trump’s base. Values they hold dear now seem smugly derided as quaint. The mainstream media comments on them but does not represent them. Even when reporters deign to visit middle America, the stories often seem written as a subtle inside joke for the coasts. It’s no wonder that people in the heartland have slowly turned to right-wing media, preferring to get their news from sources that do not treat them as dumb country cousins at a metropolitan gala.

It makes sense that Trump supporters can believe so wholeheartedly that the country is on the verge of collapse.

Unfortunately, these outlets have abused such trust by force-feeding their audiences a diet of outrage. Scroll through the constellation of fear mongering sites that orbit conservative media and try to recognize the America you know in those stories. It makes sense that Trump supporters can believe so wholeheartedly that the country is on the verge of collapse.

In the context of this fear, particularly for many who served in the military, measured tones and caution seem like political double-speak and cowardice. They know there is a real enemy. IEDs do not kill in shades of grey. They have seen their friends die to take cities they now see filled with black flags on CNN.

These and other concerns with legitimate roots turn some of my friends and family towards Trump’s aggressive stance and anti-establishment voice, even as they are fully cognizant of his massive personal flaws.

I’ve seen educated, wealthy communities descend overnight into ethnic cleansing. I’ve seen family men turned into butchers.

But what they don’t see is how tenuous it all is. I’ve spent my life since Iraq in and out of conflict zones and fragile states. I’ve seen educated, wealthy communities descend overnight into ethnic cleansing. I’ve seen family men turned into butchers. I’ve seen a charismatic reformed warlord, surrounded by capable technical advisors, steer his country irretrievably into the abyss.

I was traveling across Mali, Cote d’Ivoire, and Sierra Leone when Trump escalated his comments suggesting that he’d try to put Hillary Clinton in jail and doubled down on his assertion of “rigged elections.” People there knew exactly what he meant, because they have heard that rhetoric before. This is the language of lands without strong institutions, bereft of the mutual trust that glues our democracy together. It’s the language of civil wars.

Our choice of leaders matters. Our respect for institutions matters. Trust in the democratic process matters. Freedom of the press matters. An independent judiciary matters. And it matters that America continues to believe itself a country that welcomes “your tired, your poor, your huddled masses yearning to breathe free.”

Imagine for the moment that it would be possible to set aside Trump’s repulsive personal behavior and evaluate him on his more aspirational merits. Trump as President substantially increases the risk of grave and direct harm to American citizens.

A president has checks and balances domestically, but sits virtually unbound when it comes to global affairs. Trump has lied and contradicted himself on every major foreign policy question; demonstrated a cavalier attitude toward the use of nuclear weapons; insulted veterans and current service members; stoked ethnic and religious violence; acted in support of Putin (the single person doing the most to erode global order); repeatedly demonstrated his thin skin and personal vindictiveness; and, most damagingly, undermined the trust and institutions of our republic.

There’s nothing irreversible in America’s character that makes the country forever safe.

During the fall of the Berlin Wall, President George H.W. Bush worked tirelessly behind the scenes but was modest in public, admonishing reporters by saying he wouldn’t “dance on the wall.” Now imagine Trump in the same position, preening for the cameras, inevitably stoking tensions that would have given us war with Russia or a divided Germany.

There’s nothing irreversible in America’s character that makes the country forever safe. ISIS, as it stands today, cannot compare to the threat that someone like Trump could pose to the US. The world has not matured past the specter of global conflict or the possibility of nuclear holocaust. We are not inherently different than all those previous generations who also thought they had reached the end of major wars. For our safety and as the world’s indispensable nation, America cannot have a President Trump.

Hillary Clinton is more than simply an alternative to Trump. She has certainly made mistakes, often amplified by a lack of transparency. Moreover, the Clintons have often allowed themselves to be surrounded by a political courtier class that embodies the establishment and is rife with potential conflicts of interest. But Clinton has also routinely been saddled with negative baggage that is not her own, but instead a byproduct of an exceptionally visible and polarizing political life. She is smart, thorough, and diligent in her study of complex topics. In the foreign policy world that I know best, I believe she could be among the most capable presidents of the last century.

While I understand those who choose to vote for a third-party candidate, I believe the utter unfitness of Trump imposes an obligation to vote for Hillary. Trump must not just lose, he must be soundly defeated—so that someone of his ilk cannot be taken seriously as a potential president again. A close call could invite a slightly more palatable would-be despot, or Trump himself, to try again.

For those who say they’d rather not decide between flawed choices, I’d ask them to think about what life is like every day for our troops in Iraq and Afghanistan. They don’t have the luxury of abstaining or making a protest vote on the flawed options they see before them every day.

Our country does not ask for much in the way of national service—indeed, it should ask for more. A thoughtful and considered vote this November 8th is the bare minimum. I hope we can all do our duty. What we have is more fragile than you think.