I kinda agree with this, but...
According to a piece I read several years ago, Jimmy Carter believes abortion is wrong except under certain conditions (rape, incest, danger to mother's life), and yet allowed policy to conflict with his own religious or moral ones. So in a lot of ways he was fairly progressive, especially for a Georgian Dem in the 70s.
Castro and O'Rourke were successful at running for and holding lesser positions in locations- Castro as Mayor of San Antonio, O'Rourke as Congressperson for Texas' 16th - that have largely liberal constituencies.
Carter as governor of Georgia...well, I just looked up a few things about his early political career. He won a seat on the Georgia State Senate in 1962 and was reelected in '64, but his first run for the governorship failed.
Then he became a born-again Baptist. One might suspect this aided him in his second run at governor in a bible belt state. Also, the platform he ran on was not something you might call progressive (
Britannica states he "tacitly adhered to a segregationist approach"). However, once in office his policies lead to him appearing on the cover of Time magazine, and talk of his being part of "
the new South." He didn't run for a second term, instead announcing his candidacy for President.
So I wonder how effective a model Carter is for today's Democrats.
On the other hand, Bill Clinton is a very different topic...