The western world is getting tired of it. We saw it in Greece, in Spain, in Britain (Jeremy Corybn, a borderline socialist, won a landslide victory to lead his party and is set to win it again) and have already seen a far more left Germany, France, Sweden and Holland. America is playing catch up, but rest assured, people have had enough.
As a Spaniard who voted for Podemos, I feel I need to point out a massive difference: the US political system is designed to actively punish parties that split up and to make radical agendas pretty much undoable. Let me explain. To begin with, I need to point out that the parties rising in Germany, France, Sweden and Holland are more akin to a mix between Trump and Cruz than anything resembling "left-wing", which is slightly terrifying. In fact, a few of those parties started as reformed neo-Fascist outlets, so i don't think that's something to be jealous of.
Second, the places where insurgent left-wing parties have been most successful (Greece, Spain, Italy) are countries that -albeit with bonuses to the winner in G and I- approportion their seats in a proportional way to the vote. You get X votes, you get X seats (again, there are some distortions, but the base is that). So you actually can afford to vote for a new party. In Spain, the Socialists (the equivalent to US Democrats) got 44% of the vote in 2008 and 47% of the seats. This year, the Socialists and Podemos got a combined 43% of the vote... and a combined 43% of the seats. Fair enough! The US, on the other hand, has a First Past The Post system- or Winner Takes All. Meaning, if the Democrats split their votes according to the primary results (55-45), then the resulting two parties would end... with a combined handful of seats in Philadelphia, California and little else. Ever heard about deranged and hated Republican Paul lePage winning blue Maine
twice with 30-odd percent of the vote because the left wing split up their votes between two different candidates? That, in all levels of Government, accross all the country, times ten. And this is exactly why the Labour party is trying to kick Corbyn away, fearing a complete wipeout in the next election if they are seen as "too radical" and moderate voters choose to pick the safer-sounding Conservatives, as it already happened in the UK during the 80s.
Third, not only the US has an electoral system that punishes divisions and parties whose leaders seem too radical (see: McGovern, Goldwater), the legislative system is designed to force parties to compromise, drop part of their proposals, pass wishy-washy bargains and flip-flop inside dark rooms. Why? Because, unlike in European systems where Parliament is all-powerful and appoints and removes Governments (and usually the House-equivalent alone has that power, even if there is a Senate), ensuring that both wings are on the same page and can pass laws without too much trouble, in the US there is a complete, absolute division of powers. What does that mean? That one party with barely 41 senators (which is 41% of just 1/3 of Government) can veto every single bill from ever becoming law - even if the other party controls the presidency and has majorities in both houses of Congress. When you give veto power to such a tiny piece of the system, you are essentially forcing both sides to deal. Even if only one of the two sides becomes crazy (see: Republicans), the entire system is doomed into gridlock forever unless both sides compromise in everything.
In other words, the US Constitution was written to encourage moderate, centrist leaders who can deal in the shadows and who can appeal to the largest share of the population by not looking too extreme or radical, and to encourage a "lesser-of-evils" mindset on the voters. Thus, Hillary Clinton. Hence, Trump is tanking. Therefore, insurgent parties simply cannot grow. The US can wake up, but as long as the Constitution is intact, it won't do much good.
Also good luck changing the US Constitution.
