Obama is further left than Clinton, but that's really irrelevant to the point I'm attempting to make.
We operate in a two party system and
the Democratic party is the big tent party that covers a larger portion of the political spectrum than what you see in European style parliamentary governments which they're unfairly being compared to.
Social liberalism is still a tenant of the Dem party and the main platform. The same goes for a lot of egalitarian prolicies.
Over 2/3 of the Dem base considers themselves to be in the centrists to center left lane.
And based on polling the majority of dem voters support center left policy.
That said, the structure of our government almost guarantees party results will be somewhat centrist despite ideology.
It's not like the dems win parliament here and form government.