Did Left wing Democrats launch their own party or “tea party movement” inside the Democratic party? No, they didn’t. Sanders keeps getting elected as an independent, why did he never launch an actual alternative with candidates all over the country?
Probably because the tea party was funded by billionaires and there are no billionaires funding any left-wing movements.
That pales in comparison to the vast wealth of billionaires which is needed to fund an entire movement and not just one person. It’s easier to have one or a small handful of billionaires coordinate their wealth than to get millions of individuals to pool their money together to fund a cohesive movement.