America has just lived through another presidential campaign week dominated by Donald Trump’s racist lies. Here’s a partial list of false statements: The United States is about to take in 250,000 Syrian refugees; African-Americans are responsible for most white homicides; and during the 9/11 attacks, “thousands and thousands” of people in an unnamed “Arab” community in New Jersey “were cheering as that building was coming down.”

In the Republican field, Mr. Trump has distinguished himself as fastest to dive to the bottom. If it’s a lie too vile to utter aloud, count on Mr. Trump to say it, often. It wins him airtime, and retweets through the roof.

This phenomenon is in fact nothing new. Politicians targeting minorities, foreigners or women have always existed in the culture. And every generation or so, at least one demagogue surfaces to fan those flames.

Here’s Donald Trump on Sunday: “When the Syrian refugees are going to start pouring into this country, we don’t know if they’re ISIS, we don’t know if it’s a Trojan horse. And I definitely want a database and other checks and balances. We want to go with watch lists. We want to go with databases. And we have no choice. We have no idea who’s being sent in here. This could be the — it’s probably not, but it could be the great Trojan horse of all time, where they come in.”