In sweeping retaliation for Russia’s growing aggression in the West, the United States and nineteen other nations expelled more than a hundred and thirty Russian intelligence officers and diplomats on Monday. The coördinated rebuke—galvanized after Moscow’s alleged assassination attempt on a former double agent living in Britain—is unprecedented since the Cold War, which ended more than a quarter century ago. It sends a muscular message from the West to President Vladimir Putin that he can’t attack one Western country without generating a broad response from them all, a Western diplomat told me. But it also signals the potential for a deeper confrontation that could ripple across other global flashpoints where Western and Russian interests compete.

The showdown also has serious implications for President Trump’s hopes of improving relations with Putin, whom he congratulated just last week on his reëlection to another six-year term. “This is in many ways the end of an illusion—the illusion of some sort of grand bargain with Putin, under which Trump has seemed to operate for so long,” William Burns, a former U.S. Ambassador to Russia and now the president of the Carnegie Endowment for International Peace, told me.

Further actions by the Western alliance are also on the table, a Western diplomat told me. “Today was a pretty extensive set of measures. We’ll see what Russia does in response,” he said. “We and our allies are constantly talking to each other about how we deal with this strategic threat. The locker is not empty.” The White House said that it had not ruled out sanctions against Putin himself.

Washington took the biggest step, ordering sixty spies—forty-eight in Washington and twelve in Russia’s mission to the United Nations, all of whom had been operating under diplomatic cover—to leave the country within seven days. It also ordered the closure of Russia’s consulate in Seattle, which is close to a U.S. naval base and the headquarters of Boeing. On Monday, a sign on the consulate door said that it was no longer taking applications for passports or visas. Other nations, from Canada and Croatia to Spain and Sweden, also followed Britain’s decision, earlier this month, to expel twenty-three Russians. In all, twenty-one Western nations have now ordered the ouster of a hundred and thirty-five spies and diplomats.

“The United States takes this action in conjunction with our NATO allies and partners around the world in response to Russia’s use of a military-grade chemical weapon on the soil of the United Kingdom,” the White House said, in a statement. In a briefing, a senior Administration official said that the actions make the United States “safer by reducing Russia’s ability to spy on Americans and to conduct covert operations that threaten America’s national security.”

Russia announced that it would respond—in kind. In Washington, where early on Monday he was summoned to the State Department for official notification, the Russian Ambassador, Anatoly Antonov, called the expulsions provocative. “Very little still remains in terms of Russian-American relations,” he told a Russian news agency.

In a strange twist, the Russian Embassy tweeted, “US administration ordered the closure of the Russian Consulate in Seattle @GK_Seattle. What US Consulate General would you close in @Russia, if it was up to you to decide.” It offered options to check: the U.S. consulate in Vladivostok, Yekaterinburg, or St. Petersburg.

In Moscow, the Foreign Ministry spokeswoman, Maria Zakharova, said on national television that Britain had not provided any evidence to support allegations that Russia had used Novichok, a lethal chemical weapon that has never been used on the battlefield, to poison Sergei Skripal and his daughter Yulia in the British cathedral city of Salisbury.

Tensions between the West and Russia are likely to escalate, at least in the short term, in what could look like a “Cold War on steroids,” Nina Khrushcheva, who is the granddaughter of the former Soviet Premier Nikita Khrushchev, and who now teaches at the New School, in New York, told me. “Putin is judo-esque to the core of his being. For him, this is all a game: ‘Who’s he going to screw next?’ He wants the upper hand. He doesn’t give up. He doesn’t stand back. He sees an opening and strikes. He punches ten times what he receives. He’s a brilliant tactician but a petty man. We’ve seen that for all his eighteen years in power.”

The danger down the road, Khrushcheva said, is Putin taking broader retaliation—pulling out of international agreements, complicating foreign businesses’ operations, or expelling more diplomats and even foreign journalists. “We can’t predict exactly,” she said. “Seizing Crimea may seem shortsighted from the rational point of view. Russia got a hit in international affairs, but for Putin it was a rise in Russian patriotism. The poisoning of Skripal was shortsighted, and the timing was bad—before the elections on March 18th—but, given Putin’s view that enemies, traitors, must be punished, Russia unlikely regrets it. In essence, from a position of bettering the country, Putin is always shortsighted. But with his tactical victories he is always willing to say, ‘Russia is going to be strong, even if it means being punished by the West, even going hungry.’ ”

Others say that the diplomatic crisis could, over time, force Russia to rethink its strategy. It faces a growing economic morass, troubling demographic trends, the cost of foreign military interventions in Crimea and Syria, and diminished international standing. Putin literally can’t afford another Cold War, William Taylor, a former U.S. Ambassador to Ukraine, told me.

“This is not the Cuban missile crisis,” Tom Pickering, a former U.S. Ambassador to Russia and the U.N., added. “But there are a lot of lessons from the Cuba crisis that we should pay attention to, such as overreaction, overreliance on nuclear weapons, talking about them as if they’re something anybody can use, and a clear sense that, unless adults are truly in charge of the relationship, it can get worse without control.” He warned that the United States and its allies need a strategy with a combination of pushback and messaging through diplomatic channels at the highest level to find ways to avoid real peril.

“At the moment, it’s a game of chicken with no off-ramp,” Pickering told me. “And we need to be looking at the off-ramp.”

The new diplomatic démarche differs from previous rounds, former U.S. Ambassadors who worked in both Republican and Democratic Administrations, say. In December, 2016, President Obama unilaterally expelled thirty-five Russian diplomats for Moscow’s meddling in the U.S. Presidential election. Seven months later, in July, 2017, Moscow ordered U.S. missions in Russia to reduce their staffs by seven hundred and fifty-five people; the majority were Russian nationals banned from employment in U.S. missions. At the time, Trump thanked Russia for cutting back on the expense of keeping a larger U.S. diplomatic presence in Moscow. The largest expulsion since the Cold War ended, in 1991, was the deportation of fifty Russian diplomats after the arrest, in 2001, of the F.B.I. agent Robert P. Hanssen, who had spied for Moscow for more than fifteen years.

“It used to be expulsions were handled with a very precise decorum,” Stephen Sestanovich, a former U.S. Ambassador-at-large for the former Soviet Union, told me. “This has a different look. It’s not tit for tat. You’ve got expulsions taking place in a kind of free-form way that is meant to send signals about the broader relationship.”

The biggest difference in the new response to Russia aggression is Western unity, which is significantly stronger than its response after the Russian intervention in eastern Ukraine or after a Russian missile shot down Malaysia Airlines Flight 17, Taylor told me. “It’s so important that the U.S. and Europe and others around the world act in concert,” he said. “The effectiveness of this message—and the clarity—to the Kremlin and to the Russians is magnified when the international community, as a whole, makes it clear that their actions are unacceptable.”