Josh Rogin is a Washington Post Global Opinions columnist.

The U.S.-Russia relationship is too big to fail, but it’s failing.

The Obama administration came into office with a big idea about this relationship: that these two world powers must work together on areas of mutual interest even if they still worked against each other where their interests diverged. The concept was sound, but as relations have deteriorated and Russia has taken a more antagonistic stance, the United States has failed to adapt.

Last week’s revelation that the administration is proposing increased military cooperation with Russia in Syria, in exchange for Russian agreement to abide by the cease-fire it had already agreed to, was a stark example of how the administration’s theory about how to work with Russia is being misapplied on the ground. Washington is offering Moscow both a reprieve from the political and military isolation it imposed after the invasion of Ukraine — and a reward for taking unilateral military action designed to undermine U.S. policy in Syria.

The White House and the State Department believe that the only way to make progress in Syria is to work with Moscow, even if that means setting the isolation effort to one side. That makes some sense, but only if Russia actually honors its agreements in Syria and makes progress toward resolving the Ukraine crisis.

But neither of these things is happening. Ukraine’s recently departed prime minister, Arseniy Yatsenyuk, told me last week that while Russia has successfully distracted the world from the Ukraine crisis, the Russian military continues a medium-boil military campaign in violation of the Minsk agreement.

“Every single day they kill Ukrainian soldiers, every single day the death toll is rising, every single day we’ve got civilian casualties. There is no cease-fire on the ground,” he said.

To Yatsenyuk, Russian President Vladi­mir Putin’s strategy is clear. Russia will pretend to work with Western powers and even strike deals when the deals are sweet enough. But by selectively violating the agreements while manipulating other governments and the media, Putin will continue to make steady progress toward his anti-Western, anti-democratic objectives. For Yatsenyuk, there’s simply no way to work constructively with the current Kremlin.

“I don’t believe that you can agree on anything substantial with the Russian Federation because the U.S. is an enemy to the Russian Federation in their view,” he said. “They can have talks, they can have debates, they can even agree on some non-existential issues. But there is an existential difference. These are just two different worlds.”

The United States cannot afford to write off the U.S.-Russia relationship. There is truth to the argument that the world’s most pressing problems, including Islamic extremism, cannot be solved without some Russian involvement. But Washington cannot ignore Russia’s increasingly horrendous behavior. Russia’s dangerous military maneuvers near U.S. ships are now regular occurrences. Russian harassment and intimidation of U.S. diplomats across Europe is at an all-time high. Russian government cyberespionage and propaganda campaigns have run amok.

“The fact is, they are engaged in a new global Cold War against the U.S.,” said Samuel Charap, senior fellow at the International Institute for Strategic Studies. “There’s absolutely no question about that. We have this festering wound on the relationship that nobody on the U.S. side is spending much time trying to fix.”

The United States has complicated relationships with lots of problematic countries. China, for example, is internally repressive and externally aggressive, but there’s no thought of cutting off relations with Beijing. Similarly, the policy of isolating Russia as punishment for its invasion of Ukraine has limits. Russia was determined not to cave to sanctions, and if the recent vote in the French senate is any indication, the sanctions regime will not last forever.

“Putin is a very smart, sophisticated political animal,” said Yatsenyuk. “He can wait and wait for a quite long and extensive period of time. He knows how the Western powers act.”

The United States must establish a new relationship with Russia that is intellectually honest about Moscow’s actions and intentions while preserving whatever cooperation is possible. That may mean finding an endgame to the Ukraine sanctions before they crumble under their own weight. But it also means pushing back more against Russian provocations and raising the cost for Putin when he acts out on other fronts.

Defense Secretary Ashton B. Carter, who internally opposed President Obama’s new Syria proposal, said last week that if Russia would “do the right thing in Syria — that’s an important condition — as in all cases with Russia, we’re willing to work with them.”

The U.S. government needs to come up with a credible answer to the corresponding question: What is it willing to do if Russia continues to do the wrong things?