For starters, there are only right and extreme right policies among the Dems and Reps. Secondly, there is a massive pool of disaffected voters that would vote for a lukewarm progressive like Bernie, who was projected to even steal Trump voters, because progressive policy is popular. The Dems ran rightward and lost their voters in general.
Liberalism is the ideological backbone of Capitalism. Capitalists are Capital owners, not just supporters of Capitalism.