The US Left doesn't represent a broad enough population to win most national elections; certainly not enough to pass national law. They win local elections in places like SF or Seattle that were Harris +52 (e.g. contrast with Maduro's fake election only claiming a 9 point margin) and are over-represented in Dem party donors, which influences Dem representatives.
Nevertheless, they express extreme positions. Like "people should be treated preferentially by race" or "private property should be abolished/confiscated" or "the police should be defunded" or "transwomen should be allowed to compete in women's sports categories" or "illegal immigrants should receive taxpayer-subsidized healthcare." These are like 70-30 or 80-20 issues at the national level, with Leftists on the wrong side.
Ok. I think I adequately answered that. They're a minority faction; they can't pass laws. I think you know this, and your comment suggesting a faction must pass laws in order to be extreme (bluGill's contention) was a deliberate sleight of hand.