i'm going to take the question seriously.
you should trust me because i've worked in politics multiple times (staff for nevada state democratic party) but also disregard me because i'm an anarchist so of course i'm going to say it's not viable
[thread]
I haven't even read the thread yet but broke into my reading of it to thank you because I am also an anarchist and in addition have a lot of US political lore from a long time when I was a left-liberal, so it's good to know I'm not the only one.
I think the other component is that cities and states need people too, and you build up your bench of qualified people that way. A national-only party doesn't have that, so it always rings of vanity product. (Also, to break the 2 party system even slightly, you need to change state and local laws.)
to start talking about this, we have to ask two things: who would be the people running the party, and who would be the base of support?
let’s call it Unnamed Leftist Party (ULP)
Maybe I'm naive here, but it also seems like a lot of what one would want from a left third party is addressed by having a robust and active primary system. A lot of third party energy surely gets defused because people like AOC can get elected within the left coalition.