The Kosovo operation is a 20-year old episode, but it’s a rare example of Sanders openly, if not quite transparently, grappling with his conflicting principles—and presidents often have to do that. Sanders voted for a resolution, preferred by the Clinton administration, which “authorized” the operation without codifying that the authorization was legally required under the War Powers Act. (Sanders, and nearly all of his colleagues, voted against a formal declaration of war.) And when even that resolution failed in the House on a tie vote, Sanders did not insist the operation end on the basis of its constitutional illegitimacy. Five days later at a Montpelier, Vermont, town hall, he passionately supported the bombing.

Twenty years later, when it comes to defending NATO allies if attacked, the Blob will be happy to know Duss was unequivocal that Sanders would respond militarily: “Shared security is something Senator Sanders strongly believes in, and the principle of collective defense is at the core of NATO’s founding treaty. It’s important for friends and foes alike to have no doubt that the United States will honor this commitment.”

Beyond that, Duss told me that cases of “genocide or of mass atrocities” would “weigh heavily” on the mind of Sanders as president. And he laid out the questions Sanders would pose: “Does this meet the level of an emergency, an imminent atrocity? Does it immediately impact the security of the people of the United States? And if it doesn’t, does that imminent atrocity, rise to the level of a global norm which we have interest in enforcing and upholding? And finally, and very important, what are the chances for creating a better outcome having taken this step of introducing U.S. military forces into the situation?”