He subscribes to the “great power” doctrine. His geopolitical calculus is unfortunately ossified with regards to military action potentially escalating to nuclear confrontation. It’s a mindset he shares with a TON of older politicians on both sides of the aisle, and it’s a key reason why Putin’s saber rattling is so effective at making the rest of the world mostly not get in their way in Ukraine, and why most western leaders are still shitting their britches over every single threat Putin makes. And in point of fact, that’s the reason Putin uses the strategy in the first place. He’s playing for an audience, and the audience is 70-80ish year old western politicians who have strong memories of the worst of the old Soviet saber rattling.