If it’s common knowledge, then there is no problem. The Democrats were very smart to keep their party from being hijacked by a non party member. Lets remember, Bernie Sanders is not a Democrat.
And the Democrats are not liberals.
There is nothing pre-ordained that says Democrats must be liberals or Republicans must be conservatives. I offer Drumpf as an example.
Surprisingly you have a point. The group of 2016 democrats owe a lot to the 1980’s republicans. There was a time from 1968 to 1992 that the GOP held the White House for all but 4 of those years. Think about that; 4 out of 24 years. Then the GOP went plumb crazy with Newt Gingrich and Tom DeLay and hasn’t recovered since.
Pro Tip: When they have their post-mortem for this year trying out to figure “what went wrong”, look for the word/phrase “extremist” or “extreme” or “all or nothing” to be banished from the GOP playbook. They keep running that offense and it’s killing them.