The reality is much more complicated. The Democratic party is far from perfect (they kinda suck, in fact), and if they aren't attracting voters, "the other side is just stupid" is a useless, arrogant way to go.
The Democratic party often sounds like a bunch of elitists, and that turns off many voters, even those who might consider themselves liberal or progressive. I'll likely vote for Democrats in every election until I die, but I don't think of myself as a Democrat, and haven't registered as one in decades (fortunately the Democratic party has open primaries in California, so I don't have to declare a party).
