Even with the war in Ukraine going much worse than expected for Russia, the probability of Russian President Vladimir Putin deploying a nuclear weapon is “low but not zero,” former U.S. Secretary of Defense and CIA Director Robert Gates said Sunday.

Speaking on CBS’s “Face the Nation with Margaret Brennan,” Gates said Russia’s use of a tactical weapon would prompt a strong response from the West, including establishing a no-fly zone over Ukrainian skies. In addition, he said such a move wouldn’t “change the military equation on the ground” because Ukrainian forces are spread widely and are fierce in their resistance.

“The other thing that I hope somebody around Putin is reminding him is that, in that part of the world, and particularly in eastern Ukraine, the winds tend to blow from the west,” Gates said. “If you set off a tactical nuclear weapon in eastern Ukraine, the radiation is going to go into Russia.”

Gates, who served as defense secretary under Republican President George W. Bush and Democratic President Barack Obama between 2006-2011, said the Biden administration should have started arming Ukraine for a conflict with the Russians months earlier. But he gives President Joe Biden high marks for rallying the U.S. allies and assembling a coalition to confront Russia, resisting calls for a no-fly zone — which would require deeper intervention — and for refusing to bite on Putin’s nuclear threats.

Gates pointed out that sanctions from the West and failures on the battlefield have dealt a major blow to Russia and its global standing. “Putin will remain a pariah,” Gates said, adding: “He has put Russia really behind the eight ball economically, militarily, and because now people are going to look at the Russian military and say, ‘You know, this was supposed to be this fantastic military. Well, they give a good parade, but in actual combat, not so hot.'”

Latest developments:

►Russia pressed its offensive in eastern Ukraine on Sunday as Polish President Andrzej Duda traveled to Kyiv to support Poland’s European Union aspirations, becoming the first foreign leader to address the Ukrainian parliament since the start of the war.