In his repeated attacks on the Western alliance—culminating in a head-spinning morning with reports of Trump threatening to “go his own way,” followed by his declaration that “I believe in NATO”—Donald Trump has raised an important question: What’s the point of NATO anyway? Today, even asking that question places you on the outer fringes of American foreign-policy debate. But that wasn’t always so. Jeane Kirkpatrick, Ronald Reagan’s former UN ambassador, has a chair named after her at the Council on Foreign Relations. But in 1990, she declared, without regret, that “NATO will not survive the current reconfiguration of Europe.” Every year the American Enterprise Institute gives out an award named for Irving Kristol, the “godfather of neoconservatism.” But in 1993, Kristol wrote that NATO is on the “way to becoming moribund” as America embraces “a renascent nationalism.” This, Kristol added, “is something that most conservatives have long wished for.”

“Why NATO?” isn’t a crazy question. I can imagine four possible answers.

First: to deter a military threat from Russia. Yes, one might concede, Russia is not the military power the Soviet Union was. But it still dismembers neighbors. Just look at what Vladimir Putin has done to Georgia and Ukraine. NATO is what prevents him from doing that to Estonia.

Second: to fight terrorists and other assorted bad guys. Since the Cold War, when the United States has wanted help with a military intervention, it has often relied on NATO. When the Clinton administration couldn’t get United Nations approval for its 1999 war in Kosovo, it turned to NATO not only for legitimacy but for extra firepower. In 2011, NATO intervened in Libya. NATOtrains soldiers in Afghanistan and fights terrorism more broadly. The American public’s disillusionment with these “out of area” missions—and the virtual end of the war against ISIS—are part of what makes Trump’s assault on NATO possible today. But, one day, a new “out of area” threat might emerge that would make Americans better appreciate NATO’s help.

Third: to keep Germany docile. The irony behind Trump’s demand that Germany build up its military is that NATO was created, in part, to prevent Germany from building up its military. Twice in the 20th century Berlin launched wars of conquest in Europe. NATO was partly designed to ensure that Germany could never do so again. One can ask whether that’s still a legitimate concern given how deeply liberal democracy has taken root in German soil. To which the supporters of answer number three might respond: Why find out? The 70 years of European history since NATO’s creation have been a lot better than the preceding 50. So why mess with success?

These answers all have their merits, and their weaknesses, but none explain the terror that Trump’s attacks on NATO have provoked. That terror stems, above all, from a fourth answer, which is often more assumed than articulated: that NATO helps preserve liberal democracy among its members. When politicians defend NATO against Trump’s assaults, they almost always describe it as a bastion of democracy. Earlier this month, four Democratic senators called on Trump to “make a strong statement of support for the democratic nations that make up the alliance.” In explaining why the Senate this week passed a resolution reaffirming America’s support for NATO, South Dakota Republican John Thune called the organization “something that has served freedom-loving countries well for half a century.”

This is a little weird. It’s weird because although NATO’s charter discusses “democracy, individual liberty and the rule of law,” democracy is not a requirement for membership. Portugal joined NATO at its founding in 1949. It didn’t become a democracy for another 25 years. Between 1967 and 1974, Greece—a NATO member—was ruled by a military dictatorship. And, more relevantly today, the governments of Poland, Hungary, and Turkey have all grown dramatically less free in recent years. Yet they’re all still in NATO.

The harsh truth is that while many of Trump’s critics cherish NATO because they see it as upholding democracy and freedom, the organization hasn’t done a very good job of that lately. That’s not primarily because it has been ineffectual in countering Vladimir Putin. It’s because it has been ineffectual in countering the rising authoritarianism in its own ranks. If NATO’s supporters want to bolster the organization against Trump’s attacks, they need to think about how it can.

The best place to start is with Poland. The reason is that Poland—unlike Turkey or Hungary—desperately wants something from NATO: a long-term American troop presence on its soil. Poland, which for historical reasons remains fearful of Russian aggression, has not only met Trump’s demand that it devote 2 percent of GDP to defense. It has offered to spend an additional $2 billion to build permanent military bases for U.S. soldiers.

During an interview earlier this week, Jeffrey Rathke, a senior fellow at the Center for Strategic and International Studies who previously worked at NATO headquarters, suggested to me that America could offer Warsaw a deal. Poland gets its American troops so long as it restores the independence of its judiciary and the freedom of its press. In conjunction with pressure from the European Union, this kind of American offer might bolster those Poles who are fighting for liberty and the rule of law, and move NATO closer to being what its defenders claim it already is: the guardian of freedom in Europe.

Is such a proposal conceivable while Trump—a would-be authoritarian himself—runs the United States? No. But if his critics want to effectively defend America’s presence in NATO, they must better explain NATO’s value. And if they think NATO is valuable because it upholds democracy in the face of authoritarian threats, they must show how NATO can do just that. Poland is the place to start.