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.