A new study attributes Donald Trump's victory last year to communities hit hardest by military casualties and angry about being ignored. These voters, the authors suggest, saw Trump as an "opportunity to express that anger at both political parties."

The paper—written by Douglas Kriner, a political scientist at Boston University, and Francis Shen, a law professor at the University of Minnesota—provides powerful lessons about the electoral viability of principled non-intervention, a stance that Trump was able to emulate somewhat on the campaign trail but so far has been incapable of putting into practice.

The study, available at SSRN, found a "significant and meaningful relationship between a community's rate of military sacrifice and its support for Trump." The statistical model it used suggested that if Pennsylvania, Michigan, and Wisconsin had suffered "even a modestly lower casualty rate," all three could have flipped to Hillary Clinton, making her the president. The study controlled for party identification, comparing Trump's performance in the communities selected to Mitt Romney's performance in 2012. It also controlled for other relevant factors, including median family income, college education, race, the percentage of a community that is rural, and even how many veterans there were.

"Even after including all of these demographic control variables, the relationship between a county's casualty rate and Trump's electoral performance remains positive and statistically significant," the paper noted. "Trump significantly outperformed Romney in counties that shouldered a disproportionate share of the war burden in Iraq and Afghanistan."

The president's electoral fate in 2020 "may well rest on the administration's approach to the human costs of war," the paper suggests. "If Trump wants to maintain his connection to this part of his base, his foreign policy would do well to be highly sensitive to American combat casualties." More broadly, the authors argue that "politicians from both parties would do well to more directly recognize and address the needs of those communities whose young women and men are making the ultimate sacrifice for the country."

The most effective way of addressing their needs is to advance a foreign policy that does not see Washington as the world's policeman, that treats U.S. military operations as a last resort, and that rethinks the foreign policy establishment's expansive and often vague definition of national security interests.

"America has been at war continuously for over 15 years, but few Americans seem to notice," Kriner and Shen write. "This is because the vast majority of citizens have no direct connection to those soldiers fighting, dying, and returning wounded from combat." This has often been cited as a reason that wars don't have much of an impact on elections. The war in Afghanistan, which began in 2001, wasn't mentioned as a policy concern in any of the three Clinton-Trump debates last year. The Trump administration's internal deliberations over whether to institute a troop surge have garnered little media coverage.

When President Barack Obama campaigned for reelection in 2012, he bragged that he'd brought the Iraq war to an end and promised to do the same for the war to Afghanistan. In fact, Obama did not end the war in Iraq, a fact he admitted only after Republicans blamed the rise of ISIS on the end of the war, and the conflict in Afghanistan outlasted his tenure. His claims nevertheless received little pushback.

Meanwhile, the principle of non-intervention, when articulated by politicians like Sen. Rand Paul (R-Ky.), is often dismissed as unserious. "Simply being pro- or anti-intervention is not a useful way of thinking about foreign policy," Foreign Policy's Paul Miller wrote in 2014.

Paul did not make it far through the 2016 election cycle, though it probably wasn't his antiwar ideas that sank him. His father, the far more radical Ron Paul, performed a lot better in the 2012 Republican primaries, never wavering on the position of non-intervention. Rand tried to stake a position on both sides, hedging his non-interventionism for a base he assumed might not accept it.

As I warned in April 2015, Paul's shift toward Republican orthodoxy risked "driving away the kind of supporters probably no other mainstream candidate could attract" without convincing anyone in the establishment, which continued to call him an isolationist. Trump, meanwhile, slammed George W. Bush for the Iraq war and 9/11 at a debate in South Carolina, a miliary stronghold that nonetheless voted for Trump in its primary. Trump's on-again, off-again skepticism about America's wars led some to believe he might be a non-interventionist, though he was no such thing.

The paper by Kriner and Shen should be ample evidence that there will be space in the 2020 election cycle for a principled non-interventionist not just to run, but to win.

Related: Check out Reason's special foreign policy issue.