Russian President Vladimir Putin believes his forces are winning the nearly five-month war in Ukraine, despite failing to take Kyiv and suffering heavy troop losses, according to Tatiana Stanovaya, a Russia expert at the Carnegie Endowment for International Peace.

In an op-ed for the New York Times, Stanovaya warned that Putin will become "most dangerous" when he begins to think he's losing the war. 

"Everything is going according to plan. That's the line from President Vladimir Putin. The war in Ukraine, in its fifth month and with no end in sight, may be grueling. But senior Kremlin officials keep repeating that Russia, gaining the upper hand in Ukraine's east, will achieve all its goals," Stanovaya wrote. 

"That might seem hard to believe," Stanovaya added, "But it's what the Kremlin seems to believe."

But Stanovaya said that Putin will "face reality" sooner or later.

"It is in that moment, when his plans are stymied and his disappointment high, that he is likely to be most dangerous," she warned, adding, "For the West to avoid a catastrophic clash, it needs to truly understand what it's really dealing with when it comes to Mr. Putin."

Stanovaya said that Putin is "divorced from reality," but underscored how vital it is for the West to comprehend his goals in Ukraine. Putin has railed against previous rounds of NATO expansion two decades earlier, and in the current crisis he and top Russian officials have stoked fears they may deploy their nuclear assets, a threat that deeply concerned Western powers but that wasn't followed through on. 

Putin appears to have three main objectives at this stage of the war, Stanovaya said. The first and most "achievable" goal are his territorial ambitions in Ukraine, Stanovaya said, which are now to seize the eastern Donbas region. 

Donetsk and Luhansk provinces comprise the Donbas. Russia has fueled separatist enclaves there since 2014. In its expanded war, Russia has seized control of Luhansk, and is locked in a grinding fight with Ukrainian forces to take over Donetsk. 

"For this goal, of minimal geopolitical weight for the Kremlin, Mr. Putin appears to believe that time is on his side," Stanovaya wrote.

Putin's second goal is "focused on forcing Kyiv to capitulate," Stanovaya said, which would mean "accepting Russian demands that could be summarized as the 'de-Ukrainianization' and 'Russification' of the country."

"The aim, in short, would be to deprive Ukraine of the right to build its own nation. The government would be replaced, the elites purged and cooperation with the West voided," Stanovaya wrote.