Beto O'Rourke ran a decidedly progressive Senate campaign in 2018, especially for a Democrat running in deep-red Texas. But now activists on the left are questioning his ideology and if he's progressive enough to represent their party in 2020.
Why it matters: The left is where the energy is in today's Democratic Party. Nearly half of Democratic voters describe themselves as liberal, up 17 percentage points from a decade ago, according to Pew Research Center. After Bernie Sanders didn't get the nomination in 2016, expect the activist base that organized behind him to be even more demanding of all 2020 candidates.