Trump is unique in part because he has also defined himself in opposition to "political correctness". The purpose with this is not to further any particular law or policy; the effect is more subtle. The purpose is to fight back against strides in social decency that have been made in recent decades.Kos isn't worried so much about Trump's policies as his tone and assault on the very weak progressive edifice that was built by cultural Marxists and is maintained by SJWs.
...Any policy stance he takes is intended to force his opponents into awkward and hypocritical positions, weakening them. It should be a warning sign that his so-called "progressive" stances show far less prominence in his tone than his views on immigration, foreign policy, and "political correctness". And when Trump gets stronger, he emboldens his base. The people who view Democracy as a disease, and see women as tools for their own carnal pursuits, see their positions as gaining ground and are encouraged to push them further.
"Social decency" is a dog whistle for anti-Christian, anti-white, anti-male, anti-family views. The left must fight extremely hard to create "safe spaces" because the valuable terrain is whatever straight white males have created. They are invaders who need to put up barriers to entry in order to maintain an artificial status quo. Trump is a threat because he threatens to take all their bricks creating walls around "safe spaces" and stack them on the Mexican border. If Trump detroys political correctness, suddenly every office in America becomes a battlezone of free speech once more, a zone where the white male statistically punches above his demographic weight.
The Kos article shows the face of the rabbit. What really strikes fear in heart of the progressive is being outgrouped. They laugh at the idea of black and Hispanics voting for Trump, but he only needs to make small percentage gains, while pulling in white voters, to win a landslide. Once in office, it's clear he is more popular with blacks in terms of likability. Culturally, Trump will head a diverse coalition of anti-PC fighters. Progressive whites are pure distilled whiteness, they are more white than even white nationalists because they take white cultural traits to pathological extremes. An anti-PC Trump will make anti-PC acceptable, and this scares the rabbits because they will be outgrouped as overly sensitive, humorless, white people.
SJWs do not spend all their time on policing speech and thought for no reason. They seek total control over the public space and total obedience to whatever is the politically acceptable position of day (which could reverse tomorrow). They are rabbits seeking ingroup status because they are fundamentally insecure. There is safety in being as far on the inside of the ingroup as possible. Trump is the greatest threat because there will be no more safe spaces. Gamergate and the Puppies have shown SJWs' grip is fleeting when challenged, but a president Trump could put them on the defensive everywhere.