As a European I'm always thoroughly confused by two things:
1) That your system of government is considered democratic with only two parties. China for example has only one party and americans rightfully don't see that as a very democratic situation, so why accept it as normal back home? or to phrase it more imperialist: why not invade your own country to bring democracy?
2) The overton window. In Europe we have left and right, but they mean something totally different in the USA. Your spectrum is far more to the right. What you call left we call centre, what you call "liberal" we call centre-right, what you call centrist we call right and what you call right we prosecute for hatespeech and put on terrorist watchlists because we remember what happened here in WW II.
So as a European, Bernie Sanders seems like a reasonable centrist candidate to me. He wants to have the same healthcare system almost all other developed nations have, he wants to do at least the bare minimum to avoid catastrophic climate change as is agreed by virtually every other nation. You can imagine it strikes me as odd that these positions are somehow very progressive and unheard off. how can people even oppose those basic things? whats next? deny that humans have rights? oh wait...