People like their Blue Dog Democrats. Old fashioned Dems in the mold of Truman, JFK, even Clinton. Back in the day we had senators like tough on communism Scoop Jackson, strong on defense Sam Nunn, monetary braniac Paul Simon and civic minded nationalist Daniel Patrick Moynihan, for whom we once voted. Heck, original Algore was a Blue Dog Dem, then his wiring went wrong and he became Box Car Al*.
Anyway, these were steady, responsible men. The country knew Blue Dog Dems wanted social change, but could trust them to keep the nation strong.
When we first got into politics we were a conservative Democrat. Morton Kondrake was our favorite pundit on the old McLaughlin Group.
The country would much rather pass the Oval Office from Truman and JFK to Nixon and Bush the Elder. This rough consensus did some great things between 1945 and 2000.
Instapundit likes to say that all Dems have to do in November is not be crazy, but they can't even pull that off. Worse for them, the GOP is managing to fight off crazy this time around. See the recent WV Senate primary.
As the left goes really left, the right goes Trump and the center is left to choose. Between San Fran Nan and Trump, the center will choose Trump.
*The man once said that defense of the environment should be the 'central organizing principle' of our society. In other countries people who say things like that heard other people into box cars. Algore is the most terrifying politician of our lifetime.