Foreign and military policy needs to change along with circumstances. During the Cold War, it made sense for Washington to forge the North Atlantic Treaty Organization and make Turkey a member. Today, an American-dominated NATO makes little sense, and Ankara’s membership even less so.

Bringing in Turkey, which no one ever mistook for a liberal Western-style democracy, was always a bit of a stretch. That nation has proven over the years to be politically unstable, with occasional military interference in governing affairs. In 1974, Turkey invaded Cyprus and almost came to blows with Greece, another NATO member. Subsequent weak coalition governments were little inclined to address the country’s serious problems.

Thankfully, confrontation with Russia never came, and after the Soviet Union collapsed, alliance officials worked overtime to concoct new duties, finally settling on “out of area” operations largely unrelated to Europe’s defense. Turkey played little role in any of them (though it did contribute a small non-combat continent to Afghanistan).

As for U.S. actions, Ankara showed poor alliance relations—but good geopolitical judgment—in refusing to allow the U.S. to open a northern front against Iraq from Turkish territory in 2003. This created a rift with the Pentagon, previously Ankara’s strongest advocate in the United States. More recently, Turkey has played a largely malign role in Syria.

Early in the Syrian war, the Erdogan government allowed Islamic State personnel easy passage across its border. Smuggling was rife: Erdogan’s son-in-law and oil minister was accused of being involved in the profitable though illicit trade. In early 2018, Ankara launched an offensive against Syrian Kurds who had cooperated with U.S. forces against ISIS. In demanding the creation of a buffer zone, Erdogan even threatened to confront American personnel.

Erdogan also turned against Israel, costing him support from that nation’s advocates in America. Ankara continued to spar with Greece militarily, refusing to recognize Greek airspace surrounding islands near Turkey, and remained a major obstacle to a settlement in Cyprus. The discovery of undersea natural gas fields in Cypriot waters led to further conflict between the Republic of Cyprus and Turkey, eliciting retaliation by the European Union.

Erdogan also routinely played to widespread anti-American sentiment in Turkey, accusing the U.S. of involvement in the failed coup three years ago. Without evidence, he blamed the attempted takeover on Fethullah Gulen, an aged Muslim cleric who has lived in America for decades, and then criticized Washington for not sending Gulen to Turkey for trial, even though Ankara failed to provide the evidence necessary for extradition. Erdogan’s government also arrested several Americans, most famously pastor Andrew Brunson, on frivolous grounds, apparently to use as bargaining chips.

Misusing the judicial system was only one component of Turkey’s descent into autocracy. Ankara had already become an increasingly unfree state in which opposition to or even criticism of the president and ruling party could lead to loss of job, removal from office, and prison. The attempted coup, which some analysts suspected Erdogan of planning, provided a perfect excuse for a massive crackdown. Freedom House now rates Turkey as not free.

None of the foregoing, other than Brunson’s detention, mattered much to the Trump administration, however. The issue now threatening to break the alliance is Ankara’s purchase of Russian S-400 air defense missiles. Growing estrangement from the U.S. and Europe encouraged the Turkish leader to look east, especially after Russia’s Vladimir Putin quickly backed him during the 2016 attempted coup, and he chose the highly touted Russian anti-aircraft system over American Patriot missiles. Trump unsurprisingly blamed the Obama administration, but it was Erdogan’s decision; he may have desired better protection against American aircraft should the military again attempt his overthrow.

The Pentagon feared that the simultaneous operation of S-400s and F-35s, which Turkey planned to purchase, would improve Russia’s ability to target American aircraft in any future conflict. Undersecretary of Defense for Acquisition Ellen Lord explained: “We seek only to protect the long-term security of the F-35 program.” Despite months of U.S. complaints, demands, and threats, however, Ankara accepted the initial shipment from Russia. Washington responded by barring Ankara from purchasing the F-35.

Moreover, Washington plans to kick Turkey out of the F-35 production program, denying it some $10 billion in business. That should be sanction enough, but two years ago Congress enacted legislation instructing the president to punish nations that purchase weapons from Russia. So the administration is considering economic penalties on the Turkish government and officials.

The British Independent’s Ahmed Aboudouh apparently assumed that Ankara would fold when he insisted that “Trump’s failure to punish Erdogan further will be a lost chance to reverse Putin’s malicious agenda to implode the EU, NATO and every entity helping to keep Russia’s ambitions in check in the post-Cold War landscape.” However, backed by a nationalistic population, Ankara is unlikely to capitulate. Sanctions would just increase the bilateral hostility and possibly lead Turkey to close Incirlik air base to American operations. Turkey also could occupy Kurdish territory in northern Syria, expanding on its 2018 invasion of Syrian borderlands.

A better approach would be to eschew further sanctions and press for suspension of Turkey’s membership in NATO, with expulsion likely to follow. (Also, America’s nuclear weapons should be withdrawn from Incirlik irrespective of the resolution of the current controversy.) That would be a long overdue first for the alliance, which until now has demonstrated an unseemly desire to expand.

The only serious potential security threat to Europe today is from Russia. Yet Turkey cannot be trusted to take NATO’s side in a conflict. Ankara’s foreign policy now diverges greatly from that of the Western states, and its relationship with Russia, including cooperation in Syria, would discourage it from challenging Moscow there or elsewhere. Indeed, just as Erdogan decided that he could not trust his nation’s NATO-centric officers after the attempted coup, NATO cannot trust Turkish staff who may be budding Russophiles.

The thought of dropping Ankara creates consternation among some members of the foreign policy establishment. An unnamed “senior State Department official” insisted that “Turkey has been and remains an important NATO ally, an important partner to the United States. Our relationship is not being defined by the single issue of the S-400.” However, defenestrating Ankara would only formalize the changing relationship. In practice, Turkey has already been “lost” to the alliance. Abandoning any illusions about the relationship might better enable the U.S. to negotiate a modus vivendi with Ankara in Syria and elsewhere.

Of course, Erdogan will not be president forever. Wall Street Journal columnist Walter Russell Mead argued that “Washington should remember that Turkey is bigger than one man and focus on the long term.” Yet the U.S. should also not feel the need to chase after dubious allies whose importance has faded. Especially since, even after Erdogan’s eventual hostility dissipates, disputed interests will remain and undermine any alliance ties.

The Turkish population is already one of the most hostile to America in the world, with only 18 percent of Turks viewing the U.S. favorably in 2017. An incredible 72 percent viewed us as a “major threat.” That’s the highest level among the 30 nations polled by the Pew Research Center.

Moreover, growing Islamization in Turkey reflects popular beliefs more than government policy. That makes antagonism toward America more likely and reconciliation with Israel less likely. Previous nationalist governments have treated Greece and Cyprus more coldly and Kurdish citizens more harshly than have Erdogan’s.

The Brookings Institution’s Amanda Sloat observed: “Ankara wonders if Washington cares about its security needs, and Washington wonders if Ankara is a reliable ally.” Both answers are no. But that won’t change. It is unlikely that NATO, despite being so eager for new members, would invite Turkey to join today.

Ankara has effectively chosen to leave the alliance. The U.S. and other members should ratify that decision and work with Turkey to create a new cooperative framework when their interests align. New circumstances require new policies.

Doug Bandow is a senior fellow at the Cato Institute. A former special assistant to President Ronald Reagan, he is author of Foreign Follies: America’s New Global Empire.