Well … that was as accurate as it was depressing 
I agree that “caters” is a strong word to use. I meant something more like “the most likely party that a far-left person would vote for, and whose turnout Democrats would encourage because of that”. I agree that the Democrats with actual power generally don’t “cater” to the most radical of their constituencies, or even their elected representatives, but I would say that’s mainly because they don’t need to cater to them to get their vote; they get it almost automatically by default, and the only catering needed is to get out the vote of these people who don’t like how non-far-left the Democratic platform is, even if it’s the furthest left that has a shot.
I largely agree with you; I think the primary process is partly to blame. The primaries tend to select candidates who are middle of the road for the party. On the total political scale the candidates are as close to the extremes as the are to the middle.
Maybe I’m ignorant of the Tammany hall type corruption but that does have its advantages of potentially nominating more moderate candidates.
That’s certainly a coherent explanation.
What’s interesting is if we substitute Right for Left and Republican for Democrat(ic), the same assessment was true of the other side for many years.
But at some point in the last 15, 20?, pick your favorite number, years the R side actually did begin catering to its radical fringe. And with increasing fervor. To baleful effect for the stability of the country.
if in some future age the D side fell into that same trap of empowering their radicals, all sorts of bad stuff might happen. Fortunately there’s no evidence yet that such is coming any decade soon.
I’d love us to get us to a single transferable vote (stv) system at some point to help get us away from a strict two-party system. I don’t think we can move away from these huge big tent parties until we can really allow a bit of divergence.
I think that was the mid 90s (so 25 years ago) with Newt Gingrich’s Contract on With America. "We’ve got the majority - we can vote it in. Screw the opposition!
I think a delegative democracy system is even better and feasible with modern technology, but something needs to change.
I’ve read multiple articles on STV and listened to podcasts on the system and feel fairly comfortable with how it works. I would need to read more on delegative democracy to understand it, but I definitely agree that something needs to change.