Scott Olson / Getty / Katie Martin / The Atlantic

One’s a democratic socialist, and the other’s a right-wing nationalist. In many ways, their views on international affairs couldn’t be further apart. But in 2011, when the United States joined the NATO military campaign to protect civilians in Libya, both Bernie Sanders and Donald Trump initially seemed to support it. Then rebels murdered the country’s dictator, unleashing chaos that continues to this day. Nine years later, with Trump nearing the end of his first term as president and Sanders surging in the Democratic presidential primary, they appear to agree on something again. It’s difficult to imagine either of them authorizing a military campaign if confronted with a Libya-style crisis as commander in chief.

The shift underscores a central foreign-policy message of the 2020 presidential election: The days of the United States projecting power around the world primarily through its military are officially numbered. If the race pits Trump against Sanders, regardless of the outcome, the America that instinctively sent the cavalry to the rescue won’t be returning anytime soon.

This is the first U.S. presidential election to feature voters who were born after the Afghan War began. The “forever wars” in the Middle East have disillusioned younger generations in particular, who constitute a significant part of Sanders’s base. In different ways, both Trump and Sanders have seized on this despair. Central to the case they're making to voters is that as president, they would end these conflicts and refuse to have America serve as the world’s policeman.

“Sanders will represent, like Trump, maybe in a more civilized way, a more sophisticated way, a more predictable way, the U.S. partially withdrawing from world affairs,” Gérard Araud, the former French ambassador to the United States, told me.

Many European officials consider Sanders “a left-wing isolationist,” Araud explained. They’re as “terrified” by the prospect of his presidency as of a second Trump term, because it would sow doubts about America’s continued commitment to NATO and sustaining the U.S.-led international system.

For many in the United States and the wider world, Sanders is a relative cipher on international affairs. But since his first presidential bid, in 2016, he has developed a serious set of foreign-policy views. What most distinguishes Sanders from past American presidents and some of his competitors in the Democratic primary are his rejection of U.S. military hegemony as a means of ensuring American security and prosperity, and his determination to wean the United States off its dependence on military solutions. What will likely frustrate those grand plans, just as they have Trump’s, are unanswered questions about how realistic they are, not least during a period when the United States will contend with a rising China and resurgent Russia.

Fears that a Sanders administration would be isolationist miss what the senator is proposing, Matt Duss, Sanders’s foreign-policy adviser, told me. “Just because it’s more restrained than the aggressive interventionism of the past 20 years, Bernie’s foreign-policy vision is mischaracterized as a withdrawal from the world,” he told me.

In the 1990s, “there was a belief, especially after the first Gulf War, that we were this unparalleled military power and could use our military to achieve pretty much anything,” and that conviction yielded the disastrous Iraq War, Duss said. A President Sanders would challenge the “deeply held belief in Washington” that “unless America is at the front of every parade, the world will fall into chaos.”

Ever since entering politics in the 1970s, Sanders has focused on America’s military blunders, be it CIA-sponsored coups in Iran and Chile or the wars in Vietnam and Iraq. The stance stems from his view, consistent to this day, that his domestic political agenda is inextricably bound up in foreign policy—that runaway military spending is choking investments at home, and that corporate interests are corrupting American statecraft. He was also incensed about America’s Cold War–era crusades to overthrow leftist leaders, such as Ronald Reagan’s military support for rebels fighting Daniel Ortega in Nicaragua. (As a Senate candidate for an anti-war party in 1974, he once went so far as to call for abolishing the CIA.)

In an effort to push back against U.S. politicians who romanticize America’s foreign policy, Sanders highlights the harm caused and unintended consequences unleashed by America’s regime-change efforts. But his reading of history is also skewed in the sense that he rarely acknowledges relatively measured and effective uses of force. And it has led him to downplay the faults of those he considers victims of American military imperialism. In the 1980s, when a constituent took issue with his support for Ortega despite his rollback of civil liberties, Sanders, then the mayor of Burlington, Vermont, responded that he was worried not about whether the Nicaraguan government was “good or bad” but whether “the United States has the unilateral right to go to war and destroy a government that President Reagan and members of Congress dislike.” He’s so scarred by U.S. aggression in Latin America that he now opposes the Trump administration’s decision to withdraw its recognition of authoritarian President Nicolás Maduro as Venezuela’s legitimate leader, even though the move hasn’t involved military force.

When Sanders does praise American foreign-policy initiatives, they are of the nonmilitary variety: the Marshall Plan to rebuild war-ravaged Europe, the creation of the United Nations, the U.S.-led effort under Barack Obama to strike an agreement constraining Iran’s nuclear program. And they tend to cluster in the early years after World War II, just as his favorite prophet, Dwight Eisenhower, warned of the rise of the military-industrial complex and the corrosive influence it would have on the U.S. government’s conduct at home and abroad.

At times, Sanders seems to simply be selling a more progressive third Obama term, during which he would recommit to the Iran nuclear deal and the Paris climate accord and finish extricating the U.S. from wars in the Middle East.

Viewing Sanders as merely an extension of Obama on foreign policy, however, elides the extent to which the senator says he would shun military power in favor of diplomatic and economic tools. It also overlooks Sanders’s pledge to exercise U.S. leadership in the world according to a new (if still hazy) set of progressive priorities, including combatting climate change, kleptocracy, inequality, authoritarianism, and far-right political movements. “Instead of spending $1.8 trillion a year collectively on weapons of destruction designed to kill each other, maybe we pool our resources and fight our common enemy, which is climate change,” Sanders suggested during last week’s Democratic debate.

It’s not that Sanders is a pacifist. He has occasionally supported U.S. military operations, including a NATO bombing campaign to stop ethnic cleansing in Kosovo in the ’90s and the invasion of Afghanistan after the 9/11 attacks. But far more often, he has opposed not just military interventions, but militaristic thinking. He rejects what he considers the establishment’s shibboleths that seriousness in foreign policy is synonymous with a willingness to use force, and that force is more decisive than diplomacy.

The Sanders camp’s “evolving position” is that the United States should keep its core alliances in Europe and Asia while withdrawing militarily from the Middle East, Daniel Nexon, a scholar of progressive foreign policy, told me.

Duss said that Sanders would aim to withdraw all U.S. troops from Afghanistan, Iraq, and Syria “by the end of his first term,” and repeal Congress’s vague 2001 and 2002 authorizations for the use of military force. “We’ve watched as successive presidents have been maneuvered into staying and sending more troops, and we’re committed to avoiding that,” Duss told me. Of course, that’s also what Obama and Trump said before confronting the challenge of leaving dangerous vacuums and squandering U.S. influence in these conflict zones.

Duss contrasted his boss’s tactics and Trump’s, noting that Sanders would consult with allies and not announce changes to America’s overseas military presence “by tweet” or “treat the United States military as a paid mercenary force.” But he didn’t necessarily distinguish between their strategic objectives.

“There are real questions about the cost of maintaining these huge military presences in some of these places, so we’re definitely interested in thinking hard about whether we can reduce the number of troops in these places and still meet these [security] commitments we’ve made to these partners,” he said, when I asked about U.S. troops stationed in countries such as Japan, South Korea, and Germany. “Economically, it’s not really sustainable in the long term.”

Ro Khanna, a Democratic congressman and national co-chair of the Sanders campaign, told me that he expected a Sanders administration to continue deploying military assets to protect the “freedom of the seas” in the Persian Gulf and waters surrounding China and to “maintain some [troop] presence” in the territory of Asian and European allies.

But when I asked about Sanders withdrawing U.S. forces from South Korea in coordination with Seoul as part of a process to eliminate North Korea’s nuclear-weapons program, Khanna didn’t rule it out. And as for whether a President Sanders would retaliate militarily against Bashar al-Assad in Syria for using chemical weapons on civilians, as Trump did twice but Obama declined to do, Khanna said it was conceivable under the right conditions, but that Sanders “may think that it wouldn’t actually save lives. I think what he would focus on is, how do we get a cease-fire in Syria? How do we get regional partners to work towards a diplomatic solution that tries to end these civilian casualties?”

So what would it take for Sanders to resort to military action? His advisers say an imminent threat to Americans would prompt him to do so. He would also consider military intervention as a means of averting mass atrocities or addressing humanitarian crises abroad if it were blessed by Congress and a multinational coalition, and, as Duss put it, had “a realistic chance of making the situation better at an acceptable cost.” In practice, those would be high hurdles to clear. (“You don’t want to drone strike every brown country into the Stone Ages,” the comedian Hasan Minhaj recently inquired. “Yes, correct,” Sanders confirmed.)

Khanna added that Sanders might still be willing to take out terrorist leaders under a new and and more restrictive authorization of military force. But that wouldn’t apply to targeting state actors such as Iranian General Qassem Soleimani, who was recently killed on Trump’s orders. “You cannot go around saying, ‘You’re a bad guy; we’re going to assassinate you,’” Sanders explained during last week’s Democratic debate.

The senator has also vowed to get congressional authorization for any new military conflicts. If he honors that promise, it would effectively make U.S. military interventions highly unlikely during his presidency.

The Sanders campaign has not offered specifics about how his administration would slash military spending to free up resources for its alternative priorities, other than conducting a systematic review of the defense budget when he enters office. Nor has it detailed how it would shepherd those reductions through a resistant Congress while mitigating the economic fallout. In reality, the changes might not live up to the political revolution that Sanders says he’ll bring about. When I asked Khanna whether Sanders would advocate lowering defense-funding levels by hundreds of billions of dollars to that of the world’s second-largest military spender, China, he said he expected the decline to be more modest. “It would certainly get back to the Obama level,” he noted.

As the Brookings scholar Thomas Wright wrote in The Atlantic, progressive presidential candidates such as Sanders and Elizabeth Warren have yet to express a willingness to make the radical changes—exiting the NATO alliance, for example, or permitting U.S. allies to acquire nuclear weapons to defend themselves—that the less-militarized foreign policy they envision would require. “It is possible that Sanders and Warren find themselves stuck between the mainstream national-security worldview they have articulated and their aspirations to opt out of geopolitical competition and military interventions,” he noted. The question is just how far a President Sanders would really be willing to go in doing less militarily, especially outside the Middle East.

Trump loves boasting about how he’s built up the most powerful military in the history of the world, but he’s shown little interest in, as he put it during this year’s State of the Union address, using it to “serve other nations as a law-enforcement agency.” Even as he’s poured record sums of money into the U.S. military and launched limited strikes against America’s enemies, Trump has been just as amenable as Sanders to rethinking military interventionism and the country’s global military presence.

As Douglas Macgregor, a retired Army colonel and onetime candidate to be Trump’s national security adviser, told me recently, “Trump came to office understanding that he was at a strategic inflection point” and that “there was reason to question the wisdom of distributing U.S. armed forces all over the world in 800 bases.”

But in what should be a chastening lesson for the Sanders campaign, the president has struggled to implement his vision. He’s announced plans to withdraw forces from Syria and Afghanistan—only to reverse course amid an outcry in Washington, dispatch thousands more soldiers to the Middle East, and nearly engage in all-out war with Iran. His demands that South Korea, Japan, and European nations vastly increase their financial contributions to their U.S. military alliances have run into stiff resistance from those partners and Congress, though they have spurred NATO members to up their defense spending by billions of dollars.

“Even with how disruptive Trump has been, he’s mostly been able to freak out people and make them question U.S. commitments and U.S. resolve,” Nexon, who informally advised the Sanders campaign in 2016, said. “But how much has he changed on the ground?”

One thing that has changed is that allies are already hedging against the erosion of U.S. military alliances, whether it’s Japan acquiring new military capabilities or European nations discussing new forms of shared nuclear deterrence.

Some U.S. allies may welcome a Sanders administration over the chaos of the Trump years. “I think [Sanders] can come up with a more coherent, credible, and predictable U.S. foreign policy, albeit inward-looking,” one official with a U.S.-allied government, who spoke on condition of anonymity to candidly discuss the 2020 election, told me. “What we need from the U.S. is coherence and credibility.” Other allies, particularly those whose relationships with Trump have not been rocky, will feel differently.

“When Trump keeps asking, ‘Why do we defend Europe?’ he has a point,” Araud observed. What’s in question now for future American presidents is the very “definition of the American national interest.”

That questioning, in truth, started well before Trump. Araud recalled that when the Europeans were pressing the Obama administration to intervene in Libya back in 2011, he received a call from Susan Rice when they were representing France and the United States, respectively, at the United Nations. “You are not going to bring us into your shitty war,” he remembers Rice telling him. But eventually, Obama caved. Trump and Sanders seem determined to not do the same.

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