(CNN) - Cory Booker's theory of the 2020 case was a good one.
It went something like this: Donald Trump's presidency has deeply divided us against ourselves. What Democrats (and the country) will want -- and need -- is someone who puts optimism, unity and, yes, love forward as the antidote to the current President.
It made sense! Barack Obama ran and won on "hope and change." George W. Bush ran and won on "compassionate conservatism." Voters of all stripes want to be for something that makes them feel good rather than against something that makes them feel bad.
Booker leaned into his love message. Everywhere. At all times.
"Beating Donald Trump is the floor; it is not the ceiling," Booker said over Memorial Day weekend 2019 in Iowa. "It doesn't get us to the mountaintop. I am running for president because I want to get to the mountaintop!"
In October 2019, Booker framed his relentless positivity this way: "I was raised by parents who did not flinch in telling me about the wretchedness of life, about the bigotry, and hate, and violence," he told The Christian Science Monitor. "But they taught me that you don't combat that by abandoning your virtues, but by doubling down on them, and that that is in fact a harder way."
In every debate in which he appeared, Booker tried to keep his rivals from attacking one another -- insisting that the path to beating Trump was kindness and love, not division and anger.
And then Booker dropped out of the presidential race. Today, to be exact. "It was a difficult decision to make, but I got in this race to win, and I've always said I wouldn't continue if there was no longer a path to victory," he wrote in an email to supporters announcing the decision.
What happened? Booker miscalculated. Democratic voters were (and are) angry at the idea that Trump was elected president. They've only gotten angrier since they've seen the policies he has put in place while in office.
They didn't want an uplifting message, they wanted an undoing one. As in, the next Democratic nominee will undo all that Trump has done -- tearing it out root and branch. They want a nominee who is mad as hell and isn't going to take it from Trump anymore. And that wasn't ever going to be Booker.
The Point: Anger, not hope, is the defining trait of this year's Democratic electorate. Booker learned that lesson the hard way.