Shelby Steele writes that in the 1960s the central aim of liberals changed from freedom to moral authority.
All of America's old sins, i.e., racism, sexism, homophobia, xenophobia, etc., were being revealed and reviled, and liberals sought a way to distance themselves from that in order to reclaim moral authority. From that day to this what they seek is moral legitimacy and superiority to the bad old America, which is represented by ordinary Americans.
And so, in my opinion, a funny thing happens. Liberals become the very sort of intolerant, hateful, and even violent bigots that they decry. There is no reasoning with them, there is no debating them. Either you agree with every bullet point in their agenda or you are a bad person, worthy only of scorn and derision, which they will supply with gusto.
And so we have insane liberal policies. Four thousand shootings in Chicago last year, and the mayor announces that Chicago will be a sanctuary city. This is moral authority over reality. Liberalism is exhausted because it has become so corrupted. Hence we get Trump, the push-back to liberal morality, the President who doesn't give a flip about what they think of his morality, who wants to "abolish" political correctness. Hence we get the rabid, ferocious, crazed reaction to him from liberals. Their ideology has become a religion to them, the source of all their self esteem, and Trump is showing the world what a farce it all is.
https://www.wsj.com/articles/the-exhaustion-of-american-liberalism-1488751826 (hopefully not paywalled, the opinion section usually is not)
Here Steele explains it to Tucker Carlson:
https://www.youtube.com/watch?v=iu7kuXlL1zM