The passion of young people for Obama's campaign is fueled by the Iraq war, an uncertain economy, major concerns about the environment and global warming, and the religious right's attacks on sexuality. But more than anything it's also fueled by Obama's eloquent insistence that change is possible and that ordinary citizens can play a key role. It's fueled by the sense that Obama's personal story anticipates the story of an America that moves beyond its divisions and tackles our fundamental problems. This group also seems to resist the idea that a presidency can simply be handed down like a dynastic succession.

Participating in numbers we haven't seen in decades, these new voters fervently want Obama to win. They're reaching out to enlist their peers and volunteering to help reach others. They can be a powerful force to help him prevail.

But if Hillary Clinton is nominated, this momentum will likely crumble. The young women and men who've been flooding the Democratic primaries and caucuses will feel betrayed by a candidate who's just finished doing her best to destroy the person they've invested their hopes in. And as a result, they may simply stay home. It's not just that Hillary is running against Obama. That would be fine. It's that she and Bill and their surrogates have relentlessly assaulted Obama's character, in a scorched-earth style worthy of Karl Rove.