Over the course of the nearly seven-month war in Ukraine, Western officials and Russia experts have consistently expressed concerns that Russian President Vladimir Putin could resort to using nuclear weapons if he gets desperate enough.
Retired US Army Brig. Gen. Kevin Ryan, a former defense attaché to Russia and senior fellow at Harvard's Belfer Center for Science and International Affairs, said he's even more worried about the potential for Putin to tap into Russia's sizable nuclear arsenal now that Ukraine is rapidly regaining territory in a lightning counteroffensive that began less than a month ago.
"I have been thinking about the pressure Putin must be feeling to do something dramatic — which causes me to think again about nuclear triggers," Ryan told Insider.
Ryan said that if the occupied territories of Donetsk and Luhansk ask for accession into Russia and are accepted, it would mean "the fighting that is currently going on in Ukraine will suddenly be 'in Russia.'"
After failing to take Kyiv in the early days of the war, Russia shifted its focus to Ukraine's eastern Donbas region, which is comprised of Donetsk and Luhansk. Much of the fighting in the war has occurred in the Donbas.
The Biden administration has warned that Russia could attempt to annex Donetsk and Luhansk via "sham referenda," and were that to occur, there could be immediate ramifications if this occurred, Ryan said.
"For one, Putin could solve his military manpower problem because now all the conscripts (35+% of the force) can be used — since it's no longer a war abroad," he said.
"A second development will be that the red lines against fighting on Russian territory will be suddenly crossed," he continued. "NATO weapons will be fighting and shooting inside Russia. And most importantly, the Russian state will be under direct attack. And as we know, that is a trigger for using nuclear weapons."
Ryan, who as early as March warned of the potential for Putin to use a "small nuclear weapon," or tactical nuke, in Ukraine, said he's "even more concerned about the possibility of nuclear weapons being used now" than he was earlier.
"If we add the possibility that Russian forces might be losing hard won territory to Ukrainian forces at the same time, the pressure on Putin to do something dramatic will be enormous," Ryan added.
The former general told Insider that he shared these thoughts with senior US officials.
'The response would be overwhelming'
Lately, Russia has ceded significant gains to the Ukrainian armed forces. Ukrainian President Volodymyr Zelenskyy said that Ukraine's forces have recaptured over 2,300 square miles in the east and south of the country so far this month — an astonishing amount of territory. Until recently, the conflict was widely characterized as a grinding war of attrition with little movement on either side.