History of South America

Which term refers to a person who favors US born citizens and discriminates against immigrants?

The term you are looking for is "nativist". A nativist is a person who favors the interests of native-born citizens over those of immigrants. Nativists often express fear or hostility towards immigrants, and may believe that immigrants are taking jobs, resources, or cultural norms away from native-born citizens. Nativist sentiments have been a part of American history, and have been associated with both major political parties at various times.