“Send her back!” smells of the 1935 Nuremberg Racial Laws with which the Nazis began their elimination of Germany’s Jews — by declaring them non-German. Today, racist convictions that bloodlines determine intelligence and character are more common than usually admitted.

Trump’s rally focused on the Other, the eternal foreigner. Its chant is of a piece with Trump’s efforts to build a wall, end asylum, cage children, round up aliens and put a citizenship question in the census. Chanters denied citizenship rights to Rep. Ilhan Omar (D-Minn.), who arrived as a 10-year-old Somali refugee in 1992 and was naturalized in 2000.

The other three of the “Squad” are also first-term Congress members “of color” (although what would you call Ocasio-Cortez?) but U.S.-born, although Trump indicated that all of them should return to their countries of origin. Ironically, Rep. Ayanna Pressley’s (D-Mass.) American bloodlines go back centuries longer than Trump’s; all of his grandparents were born abroad.

Today’s overheated rhetoric resurrects the classification of people by race. Hyped by politicians, stereotyping is running amok, dangerously corroding the culture that sustains democracy. Classifying people by race destroys equality, pluralism, tolerance, civility and national unity, weakening the U.S. domestically and internationally. It will take years to repair.

Using the racial pseudo-science of the day, the Nuremberg Laws classified anyone with three or four Jewish grandparents — never mind if they were baptised Christians (e.g., Mendelssohn) — as non-German and ineligible for citizenship. Someone with two Jewish grandparents might — after physical examination and skull measurement — be declared a citizen but of mixed race. Those with only one Jewish grandparent were counted as partly German.

Anthropologist Ashley Montagu’s 1942 “Man’s Most Dangerous Myth” challenged the prevailing conventional wisdom — and not just in Nazi Germany — that race determines intelligence and character. American liberals such as Teddy Roosevelt and Woodrow Wilson embraced it as if self-evident. Our Jim Crow laws were praised and studied by the Nazis, who modeled their racial laws on them.

The Native American Party, the Know Nothings (the name could be used today), targeted Irish Catholics fleeing the potato famine in the mid-19th century; they faced terrible discrimination. Nativism flared again with the 1882 Chinese Exclusion Act and the extremely restrictive 1924 Immigration Act, aimed at keeping out southern and eastern Europeans, in place until 1965. Many Jews denied refuge in the U.S. perished in the Holocaust.

Nuremberg whiffs arose at the White House when Kelleyanne Conway demanded a journalist state his “ethnicity.” He was Jewish, as she well knew. She seemed to be stereotyping Jews as inveterate liberals. Sounds like anti-Semitism. Perhaps ethnicity could be stamped on White House press passes.

That might run afoul of current law, which prohibits listing race on identification papers such as driver’s licenses. Racial designation on IDs in the old days contributed to discrimination and segregation. Russian internal passports list “nationality” (Russia has over 100), which encourages separatism. Tatars, Chechens and Kalmyks may demand their own country. Educated Russians envy our absence of ethnic identification.

My first driver’s license long ago listed me as “caucasian,” under the old mistaken theory that Europeans originated in the Caucasus. (They didn’t. Genetically, Europeans are just bleached Africans.) For statistical purposes, forms may ask to list your ethnicity — I put in “Aleut” (prove that I’m not) — but mixed-heritage people increasingly want to be called American. It’s the logic of America. Good.

Conway, Ivanka and others warned Trump of backlash over the “send her back” chant, so he briefly disavowed it. But he started it with his “go back” tweet and relished the 13 seconds of the crowd’s roar. Trump carefully inserts white-identity dog whistles in his talks, which his base picks up and amplifies.

The political positions of the Squad are fair game. They place themselves on the far left of the Democrats and could cost the party votes in 2020. Many in both parties who affirm their citizenship and elected legitimacy still criticize the Squad’s progressive stances. Adding to “foreignness,” the fact they are women, nonwhite, young, radicals and Democrats gives Trump and his base a sixfold target.

Trump times his attention-getting outbursts to distract from damaging implications. “Go back” came as SDNY brought new charges against his onetime party pal Jeffrey Epstein. Special Counsel Mueller’s congressional testimony was set for that very day but was delayed. The 2016 WikiLeaks on Secretary Clinton appeared hours after the Access Hollywood tape and helped Trump deflect attention.

Trump has long used racial antipathy. He demanded the death penalty for five nonwhite youths wrongly convicted of rape in Central Park in 1989 and freed in 2002, but Trump never apologized. In 2011, Trump started his presidential bid by embracing birtherism. In 2016, he curtly conceded that Obama was born in the U.S. but never apologized. Trump never apologizes for anything and will keep using race. Will it work in 2020?