Because Trump is the only one who speaks this way, he can count on support from the darkest elements of American life. He doesn’t need to actually advocate racial homogeneity, call for a whites-only sign to be hung at immigration control, or push for expulsion or extermination of undesirables. Because such views are verboten, he has the field alone, and he can count on the support of those who think that way by making the right noises.
What’s distinct about Trumpism, and the tradition of thought it represents, is that it is non-leftist in its cultural and political outlook and yet still totalitarian in the sense that it seeks total control of society and economy and places no limits on state power. The left has long waged war on bourgeois institutions like family, church, and property. In contrast, right fascism has made its peace with all three. It (very wisely) seeks political strategies that call on the organic matter of the social structure and inspire masses of people to rally around the nation as a personified ideal in history, under the leadership of a great and highly accomplished man.
Trump believes himself to be that man.