The stakes behind Ukraine's surprise attack inside Russian territory

Ukraine's surprise thrust into Russia – armored columns slicing through unprepared defenses, seizing towns and settlements – is perhaps the most audacious gamble in more than two years of war, since the invasion was launched by Russian President Vladimir Putin. "There's a big psychological blow here to the Russian mindset, specifically Putin, where you have a Ukrainian penetration of Russian territory, [for the] first time since World War II," said former Joint Chiefs Chairman Mark Milley.

But Milley points out the 500-square-mile bulge is barely a dot on the map of Russia. And with three exposed flanks, it comes with considerable risk. "The Russians could mass forces, cut them off and overrun the Ukrainians," Milley said.

Asked if he expects Putin to launch a major counter-offensive to take back Russian territory, Milley replied, "That's at least one of the possibilities that could very well happen in the coming months."