Replacing institutions externally isn’t nearly as easy as rebuilding them internally. A new party in a country where a vast majority votes along traditional family lines is not going to gain any momentum in the time frame that the US needs to correct course. They’re a lot better rebuilding dems internally and keeping the existing external branding. It’s the internet so here’s my uneducated and uninformed opinion: a more progressive offshoot of the Democratic Party external to it only makes sense if the Dems win a few elections on the trot. Otherwise it’s just going to be the same as cutting one’s nose to spite their own face.