Bill Clinton said in 1995 what Trump is saying today on immigration. And Clinton said it to a standing ovation (see video below). The only difference is Clinton did not follow through while Trump is.
Compare the responses of liberals then and now. What this shows is that liberalism today has become a totalitarian subculture with mores and taboos that are impervious to reason, law, or fundamental American traditions.
The existence of this subculture is proved by the fact that ~90% of US academia and MSM is liberal. This is not a diverse subculture open to a variety of views. Rather, it is a closed cult-like subculture that blames, ostracizes, and attacks its opponents.
A real civilization is open to all ideas, willing to examine them on their merits. The legal and political rules of American civilization provide for just that by protecting the rights of individuals to say and think what they want.
A totalitarian subculture does not do that. Instead, it insists on its ideas as being the only valid ones while working to destroy the civilization that has allowed it to grow into a monster. The weak point of the American system is it protects individual rights but has few means to prevent uncivilized subcultures from taking over important parts of American society, thus subverting its core values and ideals.