[monkeyodeath]

The poll mentions "patriotism", not "nationalism", and I think those are two different things. "Nationalism" increasingly refers to an exclusivist mindset, whereas "patriotism" at least used to be more "pride in one's country".

Older people grew up during the Cold War, when the USA perceived itself as a bulwark of freedom and democracy in a world of opaque, totalitarian regimes, and when the country was further ahead than most of the rest of the world in development.

These days, a lot of the rest of the world has caught up, and a lot of younger Americans feel discouraged about the state of democracy in their own country. We aren't at the vanguard of freedom and functional government anymore.

Plus, over the past few decades, "patriotism" has been increasingly associated with flag/anthem worship, military boosting, and a kind of rah-rah "USA! USA!" attitude that has little to do with freedom and democracy. It's been turned into a marketing tool and a cudgel that right-wing political groups have used against their opponents since the Vietnam War.