The truth is there's very little the Democrats can bring up without splitting their party.
I agree.
I think the truth is, the 'moderates' have abandoned both parties as regular members. The moderates will still vote at election time, but they don't really vote in primaries or participate in party building between elections.
Which leaves only the fringe Ls as the basis of the D party. And to please them, you gotta pretend to believe some crazy stuff! Which will kill them come time for the general election.