In the US Republican and Democrat (with a capital letter) aren't used to talk about political leanings, it's ok to call the Democrats by their name while also keeping in mind that they're mostly conservatives by international standards, it makes it much easier to understand what you're talking about than "Republican-lites".
At least Sanders and the likes don't care much for the establishment so they do come out and say things that go against what the Democrats platform is. They're much more like the Cheney (Dick and Liz) that announced they wouldn't vote for Trump than they are like Haley that doesn't have the guts to actually say she lost to a sociopath.