Brendan Neill explains at The Spectator:
It happened because you banned super-size sodas. And smoking in parks. And offensive ideas on campus. Because you branded people who oppose gay marriage ‘homophobic’, and people unsure about immigration ‘racist’.
Because you treated owning a gun and never having eaten quinoa as signifiers of fascism. Because you thought correcting people’s attitudes was more important than finding them jobs. Because you turned ‘white man’ from a description into an insult. Because you used slurs like ‘denier’ and ‘dangerous’ against anyone who doesn’t share your eco-pieties.
That’s part of it, anyhow. But it also happened because conservatives refused to fight for the nation or to conserve anything. It also happened because neocons invaded the world while inviting the world. It also happened because corporations set up factories in China and hired H1B foreigners instead of employing Americans. It also happened because Churchians decided it was more important to spare the feelings of non-Christians than obey the teachings of Jesus Christ and the Bible.