There are 18 Democrats running for president. Why do new candidates keep throwing their hats in the ring?

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California congressman Eric Swalwell. Photo credit: JD Lasica/CC 2.0, via Flickr

Eighteen candidates have announced their bid for the Democratic nomination in 2020. We hear a lot about Bernie Sanders and Kamala Harris, the top two fundraisers in the race for the Democratic nomination. Other big-name candidates like Warren, Booker, Bootigieg, O'Rourke are also well known. But then there are candidates who barely register in most polls so far, like Hawaii congresswoman Tulsi Gabbard, former tech executive Andrew Yang, and California congressman Eric Swalwell. The odds are against these candidates, so why are they running?