Trumpism is the latest manifestation of the hostility to foreign things that keeps cropping up in America’s history. Our history is one of immigrant waves that are denounced, become assimilated, and join in denouncing the next immigrant wave. Hostility is especially strong when the country seems threatened. During World War I speaking German could get you in trouble; during World War II over 100,000 Japanese Americans were put in concentration camps without so much as reasonable suspicion of anything.
His campaign is based on an exclusionary form of cultural Americanism. His calls for trade barriers and physical barriers, his opposition to refugees, and his “Make America great again” slogan are all parts of it. It’s not just him, though; all or nearly all of the Republican candidates (including Rand Paul!) have played on anti-immigrant sentiment. If anything, his opponents don’t consider him sufficiently anti-immigrant; Rubio has denounced him for allegedly hiring undocumented Polish workers. (It was his contractor who hired them, and they may have been cheated of their pay, but what Rubio objects to is that they were paid at all.) A high school basketball team in Iowa has reportedly been chanting his name to mock Latino opponents. David Duke has expressed his support of Trump, who at first disavowed the endorsement but then turned around and claimed to know nothing about Duke.
Some old, ugly, unreasoning traditions are the heart of Trumpism. They’d exist even without him; he’s brought them out into the open.