Eighty years ago last month, the S.S. St. Louis entered American waters.

The liner carried more than 900 Jewish refugees fleeing Nazi persecution, hoping to find a haven across the Atlantic. Passengers had purchased landing certificates and transit visas issued by the Cuban government, and most planned to wait in Cuba while their U.S. visa applications were processed. But the Cuban government was roiled by political infighting and fearmongering that Jewish refugees might be communists. Officials turned nearly all of the passengers away.

The St. Louis sailed to Florida, coming so close to U.S. shores that passengers could see the lights of Miami. Passengers cabled President Franklin D. Roosevelt to ask for refuge but never heard back.

America — where similar nativist and anti-Semitic rhetoric had infected the public — also turned the refugees away.

The ship returned to Europe, where a handful of countries had agreed to take in the passengers. But a quarter of the ship's original manifest died during the Holocaust.

Last week, while Americans continued our endless debate about whether President Trump's bigoted rhetoric put immigrants in danger, his actions should have left no doubt. The administration announced that it was gutting the U.S. asylum system, effective immediately, by rejecting any new arrivals who had not first sought asylum in another country they passed through on their way.

This change violates both domestic and international law and is being challenged in court. If allowed to stand, it will force thousands risking all to reach the U.S. border to return to dangerous conditions in their home countries or in Mexico.

Also last week, Politico reported that the administration is considering zeroing out refugee admissions from around the world next year.

There is, however, at least one key way that today's immigration policies differ from those in the dark period of the 1930s — and, in fact, are arguably worse.

Our moral obligations to the world through asylum and refugee policy were only legally formalized in the postwar years, after the Holocaust had "shocked the conscience" of many Americans.

"We were in a sense making up for the mistakes we had made in the run-up to World War II," says Morris Vogel, a historian and president emeritus of the Lower East Side Tenement Museum.

Today, we know exactly what we're doing when we turn refugees away. Today, we know what happens when the "doors (are) closed" to a persecuted people, as White House senior adviser Jared Kushner's grandmother, a Holocaust survivor, put it in her own oral history.

U.S. policy toward displaced or persecuted peoples has never been generous. But adjusted for the lessons that history now affords us, rarely has it been so deliberately stingy.

Catherine Rampell's email address is crampell@washpost.com. Follow her on Twitter, @crampell.