Last 'respectable' Dem candidate I can think of was Harry Truman. And that was in my life time.
Truman tried to be an honest American president, yes.
JFK made mistakes and had a lot of shortcomings but did seem reasonably loyal, too, for whatever its worth. Lieberman (who the commies ran out of the D party) was too liberal for my tastes but looked honest and loyal and willing to defend America. There were a couple more that I think could pass the “respectable” test...but YES, your point is well taken... the D’s have had some pretty awful candidates (and just nominating Carter and Obama should condemn the D party to a very low level in Dante’s Inferno...! My Lord how could such terrible things happen to us in this great country!?)
HST took office about 2 months before I was born and left office when I was 7.