International

Among the first world leaders to congratulate President-elect Donald Trump was Vladimir Putin. And why shouldn’t he?

Just when relations between Russia and the West are at their most precarious point since the Cold War, Mr. Trump has been Russia’s defender and the beneficiary of Moscow’s efforts to influence the presidential campaign. At times he has seemed almost intoxicated by the Russian president, praising Mr. Putin’s firmness and insisting that the two could resolve any differences if they met. Meanwhile, he has shown little concern that Russia poses a major strategic challenge.

Few experts believe that Russia wants war with the West, but many worry that Mr. Putin’s aggressive behavior as he tries to revive Russian greatness (thus masking problems at home) could result in the kind of dangerous miscalculations that often lead to armed conflict.

Russia’s hacking of the Democratic National Committee and the Clinton campaign to interfere in the election was brazen. Even worse were actions that threatened human life and global stability, like Mr. Putin’s airstrikes against civilians in Syria, his positioning of nuclear-capable weaponry near Poland and the Baltic States, his annexation of Crimea and the war he waged in eastern Ukraine. He violated the 1987 Intermediate-Range Nuclear Forces Treaty by producing a ground-launched cruise missile and canceled a 16-year-old accord on reducing stockpiles of weapons-grade plutonium.

Despite this behavior, despite the obvious need for the next president to be alert to Mr. Putin’s mischief and to be willing to resist it, Mr. Trump has so far been Mr. Putin’s apologist.

Mr. Trump has dismissed the intelligence community’s finding that Russia was behind the hacking, displaying a disrespect for the facts and for the security institutions that compile them. On Thursday, a senior Russian official admitted that the Kremlin had been in contact with Trump allies during the campaign. While it’s not unusual for presidential campaigns to be in touch with foreign leaders, the situation raises heightened concerns given the hacking and the connections between a former senior Trump campaign official and the pro-Russia former president of Ukraine.

Since Mr. Trump has refused to criticize the Kremlin, it’s important that Mr. Obama figure out, before he leaves office, how to punish Russia for the hacking in a way that demonstrates Washington’s determination to resist cyberattacks without further escalating the conflict. Getting the balance right will not be easy. Mr. Obama should also keep talking with Russia on mutually acceptable cyber-deterrence guidelines that set rules for regulating, defending against and deterring malicious intrusions in cyberspace.

The deteriorating relationship between Moscow and Washington is a long way from what was envisioned when the Soviet Union collapsed in 1991 and there were high hopes that Russia would become a democracy integrated with the West. In 2009, Mr. Obama authorized Hillary Clinton, his first secretary of state, to “reset” relations, aiming to foster cooperation.

The two sides worked together on an arms control treaty and the Iran nuclear deal, but on the whole the reset failed, largely because of Mr. Putin. Restoring Russia to power and to a central role in world affairs turned out to be more important to Mr. Putin, and the Russians, than peaceful or profitable ties with the West. His foreign policy is a fairly consistent continuation of Soviet policy — preventing Western encirclement by moving into Ukraine; fighting proxy battles to support Russian interests, as in Syria; and challenging American power wherever possible.

Mr. Obama was slow to recognize Mr. Putin’s revanchist mission, as were other Western leaders. Now that the threat is obvious, America and its allies cannot afford for Mr. Trump to make the same mistake. What’s needed is a pragmatic review of American-Russian relations that includes, at a minimum, a reaffirmation of America’s commitment to NATO, which Mr. Trump disparaged during the campaign, and to European democracy. Mr. Putin is working to undermine both.

Achieving the right balance between firmness and conciliation has never been an easy task for the United States or its Western allies. The alliance has largely been unified in supporting sanctions on Russia for its actions in Ukraine and in agreeing to deploy military battalions of 800 to 1,200 multinational troops in Poland, in Lithuania, in Estonia and in Latvia, in addition to a brigade of four more battalions to be based in Romania and Bulgaria. Additional moves may be still be required.

Even so, the relationship between the United States and Russia cannot be allowed to slip back into a poisonous Cold War-like rivalry. The Kremlin’s receptivity to working with Mr. Trump could be exploited to serve a useful purpose. Maybe Mr. Trump will have enough influence with Mr. Putin to persuade him to adhere to arms control agreements and come back into compliance with those Russia has breached.

In many ways, Mr. Putin appears strong, but he is playing a weak hand, as Russia’s oil-dependent economy shrinks, its population ages and the country remains mired in costly military operations in Syria and Ukraine. He needs to have no doubt that the United States and its allies will defend their principles and values even as they remain open to cooperation when the interests of the two sides overlap. That is the core of Mr. Trump’s challenge.