Former President Trump has repeatedly said undocumented immigrants are "poisoning the blood of our country," language echoing the rhetoric of white supremacists and Adolf Hitler.

Why it matters: The phrase "poisoning the blood of our country" has a deep racist and antisemitic history, and the comments come as some Republicans have openly endorsed the once-fringe and racist "white replacement theory."

At least four times in recent months, Trump referred to immigrants as "poisoning the blood" of the nation.

• He said it during an interview with a right-leaning website in September.
• He said it again at a rally in December in New Hampshire.
• He repeated it in a Truth Social post in December, then again at a campaign stop in Iowa.

Trump also claimed, with no evidence, that the migrants were terrorists or from mental institutions and cited Asia and Africa as places from where they are "pouring in."

• In response to the comments, fellow Republicans so far have offered tepid disagreement or even openly endorsed the Nazi-era rhetoric, Axios Sneak Peek author Zachary Basu reports.
• Sen. J.D. Vance (R-Ohio) called Trump's comments "objectively and obviously true to anybody who looks at the statistics about fentanyl statistics" — and slammed comparisons to Hitler as "preposterous."

Reality check: The remarks "poisoning the blood of our country" are straight out of Hitler's 1925 autobiographical manifesto, "Mein Kampf" — his blueprint for a "pure Aryan" Germany and the removal of Jews.

• "All great cultures of the past perished only because the originally creative race died out from blood poisoning," Hitler wrote.
• "He poisons the blood of others but preserves his own blood unadulterated," Hitler wrote of Jewish males allowing Jewish females to marry white Christians.
• "Whenever Aryans have mingled their blood with that of an inferior race, the result has been the downfall of the people who were the standard-bearers of a higher culture," he wrote in another passage.

Flashback: Hitler ruled Germany under a dictatorship between 1933 until his suicide in 1945. He sparked World War II and was responsible for the death of at least 6 million Jews and other religious and racial minorities.

The Trump campaign did not respond to requests for comment.

Zoom in: Trump is evoking Nazi rhetoric no matter what he claims, Robert P. Jones, founder of the non-partisan Public Religion Research Institute, tells Axios.

• Trump said he's never read "Mein Kampf" and was not quoting the German dictator when talking about undocumented immigrants.
• But the "whole notion of blood and soil is taken directly from Hitler's attempts to connect his bigotry outside of the major metropolitan areas into the farmlands. Period," Brian Levin, the former director of the Center for the Study of Hate and Extremism, tells Axios.

The big picture: Trump is also evoking an old racist ideology that the Americas were designated by God as only a Promised Land for European Christians and that people of color don't fit or have to be subjugated, Jones said.

• "One only has to ask who Trump has in mind when he says 'our country' to see the connections," said Jones, author of the newly released book "The Hidden Roots of White Supremacy and the Path to a Shared American Future."

Zoom out: The population of undocumented immigrants in the U.S. is becoming more diverse, and Mexicans now have the smallest share they've ever had, according to a recent study by the Pew Research Center.

• Geopolitical conflicts, climate change and more sophisticated smuggling networks are driving more migrants from Central America, the Caribbean, South America, Asia, Europe and sub-Saharan Africa to make dangerous journeys to the U.S. without permission, absent many legal options for entry.
• The humanitarian crisis of more migrants at the border is putting a strain on an already short-staffed U.S. Customs and Border Protection agency and on cities where migrants are being bussed.

Of note: Trump's senior White House adviser Stephen Miller encouraged the conservative website Breitbart to promote white supremacist ideas and referenced "The Camp of the Saints," according to an investigation by the Southern Poverty Law Center.

• The French dystopian novel uses racial stereotypes and calls for violence in depicting the fall of white Western civilization because of migration from South Asia and Africa.

Go deeper: It's not just Trump: How racism shadows the GOP campaign