The US was founded on crime. We are a colonial imperial country with a penchant for using racism and religion in order to maintain a certain lifestyle for white supremacists.
Slavery was really not that long ago, we are still actively invading countries and murdering people for oil, and we help bankroll straight up genocide in regions such as Darfur and Palestine.
People had nearly a decade of experience with Donald Trump as a known political entity and decades of receipts and lawsuits prior to 2016 to speak to his amoral and corrupt nature. If they didn't know exactly what they were buying into they were idiots. He isn't exactly a master manipulator.
Also, The first time Trump was elected, the majority of voters went for Hillary Clinton. Second time, it was still 49% versus 48% for Kamala Harris. The majority of Americans have never voted for Donald Trump nor ever supported him.
You asked, "Whats wrong if US population has voted for this?" in response to someone complaining that the system is not working, and so I explained it: the rest of us are not represented. I'm unsure what point you're getting at.
My point is: presidents are not delivered to your country by president delivery alien space ship. A lot of people voted for him and this is a fact. You cant just blame everyone of them for being dumb or racist. If you dont like their choice that means you should starting to do something about it.
Authorithorianism also not just happen - it take years to build and destroy institutions. It took 20 years to build fascist regime in my country.