Russia-US nuclear war is no fantasy, says Kremlin ally

Russia has the world's largest arsenal of nuclear weapons. But from Moscow's perspective, the atomic deterrent was not enough to keep the US and its NATO allies from backing Ukraine against Russia.

That was unexpected since the Kremlin views this as a Western intervention in a proxy war that is strategically vital to Russia, Dmitri Trenin, an ex-Russian intelligence colonel and former director of the Carnegie Moscow Center, tells Ian Bremmer on GZERO World.

For Trenin, all nuclear bets are off if the trajectory of the conflict leads to direct military conflict between Russia and NATO.

"If there is such a collision, then (...) a nuclear exchange between Russia and the United States may not be seen as a fantasy," he says. "This is my worry."

Watch the full interview with Trenin in the season premiere of GZERO World with Ian Bremmer's sixth season. airing on US public television nationwide. Check local listings.