Former deputy national security adviser K.T. McFarland told Fox News Digital that Russia has fallen back on "Plan D" after failing to maintain a protracted siege in Kyiv. 

Russia re-evaluated its strategy and on March 25 began to pivot focus toward securing eastern Ukraine, which culminated in the surprise withdrawal from Kyiv and surrounding cities – a move that some intelligence and military experts claim is little more than an attempt to save face after a military disaster. 

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"Their Plan A was to mass along the border as if to invade, and assume Ukraine would capitulate on NATO membership and Donbas," McFarland said. "When Ukraine did not, Russia’s Plan B was to invade and be in control in a few days."

"When that didn’t happen Russia moved to Plan C – protracted war and siege," she continued. "When that didn’t work, they’ve moved to Plan D – consolidate in east and a frozen conflict along the border: spin it as a success back home, come back for rest of Ukraine in a few years." 

McFarland said the prevailing belief – hers included – prior to the invasion was that Russia would aim to take the Donbas/eastern provinces. She labeled the full invasion a Russian intelligence and military failure, stressing that Russia failed to anticipate the Ukrainian leaders and people. 

"Presumably, they thought Ukrainian leaders had been bought and would flee, and Russia could install a puppet government," she added. 

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Fredrick Kagan, director of the Critical Threats Project at the American Enterprise Institute, went a step further and said the Donbas region was little more than a "consolation prize" to make up for the "sacrifice" in Putin’s campaign. 

"The overall objective of the invasion was to replace the Zelenskyy government with a government that Moscow could control," Kagan said. "That effort has failed."

Kagan explained that the "Putin World" explanation is that Russia has "bizarrely" claimed to have achieved its objective around Kyiv and is now working to secure the land claimed by proxy republics Moscow has recognized

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But securing those regions could provide a long-term purpose, which is to continue eroding Ukrainian territory and improving future invasion efforts. 

"The more Ukrainian territory Russia has the harder it is to keep an independent Ukraine alive over time, and the more opportunities Putin will have to invade again after he’s built up his military or to do other things to achieve his aim to bring down an independent Ukrainian government," Kagan argued.

The extreme losses in Ukraine have pushed Russia to "frantically" rush to build up the military again, with a more robust conscription effort and other short-cut methods that will allow them to field something of an army.

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Ultimately, Kagan believes that as long as Putin or "Putinism" remains dominant in Russia, it will continue seeking to destroy an independent Ukraine.

"This was never about Donbas, and it’s also never been about NATO, primarily," Kagan said. "[Putin] does not accept Ukraine has the right to an independent government, he does not accept Ukraine’s sovereignty and he does not accept its existence as an independent state."