"America first" isn't a code. It's a dog whistle.

You have the people who voted Trump because of economic concerns. Even these often hold racist views, but they're a (wrong) response to the situation they're in. It's the response forced down their throats by those in power, because it's simple, not very abstract, easy to understand, and of course: benefits the powers.

Then you have all those racists, who have literally nothing to cry about.

It seems that people tend to say that it is either (A) entirely due to racism or (B) entirely due to economic anxiety, when it's really neither. It has to do with (A) being proposed as a solution to (B), an actual problem in the "fly-over states".

Historically and present, racism has been used as a tool of the bourgeoisie. It is a super smart way of killing revolutionary spirit among the working class, because nothing works better than dividing them, distracting from the real problems. By telling them that migrants or other races screw them over, they are less likely to think that the rich are those who are screwing them over.