The Wikipedia definition would be something like this:
Racism is prejudice, discrimination, or antagonism directed against someone of a different race based on the belief that one's own race is superior.
So comments on the lines of these immigrants all come from a defective gene pool, they are all inbred, they all have IQs between 60-80, they are worthless and could not possibly make any contribution to our society all fit.
Another example would be this:
“When Mexico sends its people, they’re not sending their best. They’re not sending you. They’re not sending you. They’re sending people that have lots of problems, and they’re bringing those problems with us. They’re bringing drugs. They’re bringing crime. They’re rapists. And some, I assume, are good people.”
–Real estate mogul Donald Trump, presidential announcement speech, June 16, 2015