President Trump’s more sophisticated supporters in places such as Washington and New York claim that his presidency is a raging success because he has appointed conservative judges, cut taxes and turbocharged the economy. Trump himself evidently disagrees, because he is not running the midterm campaign based on his supposed achievements. Instead, Trump and his fellow Republicans are closing the election with the most naked appeal to racial prejudice since the dark days of Jim Crow when Democrats in the South would compete to display their fervor for segregation.

On Halloween, the Trump campaign released a commercial featuring a cop-killing undocumented immigrant named Luis Bracamontes. It has been compared to the 1988 Willie Horton ad. But that is unfair. This is much worse. “Democrats let him into our country,” the ad says. “Democrats let him stay.” Actually, Bracamontes entered the United States when George W. Bush was president, and he was arrested and released by Trump’s favorite sheriff, Joe Arpaio of Maricopa County, Ariz.

The ad goes on to show hordes of unidentified people rushing a fence. It looks like a scene of a zombie attack from “World War Z” and is meant to convey the impression that the United States is being overrun by hordes of illegal immigrants. In reality, apprehensions of illegal migrants along the southern border are down more than 80 percent since 2000. There is no immigration crisis. There has been an increase in illegal border crossings from 2017 to 2018, but that’s not Democrats’ fault, since Republicans control all three branches of government. And there is no crime wave by illegal immigrants. They commit fewer crimes than native-born Americans.

In their final pitches, candidates are selling fear, hope and independence. But Trump's ad is missing the president. (Gillian Brockell, Paul Waldman, Kate Woodsome, Danielle Kunitz/The Washington Post)

But Trump acts as if a caravan of perhaps 3,500 bedraggled, impoverished refugees is an invading barbarian horde that he says might be paid for by Jewish billionaire George Soros — precisely the conspiracy theory that motivated a white supremacist in Pittsburgh to slaughter 11 people in a synagogue. “If you don’t want America to be overrun by masses of illegal aliens and giant caravans, you better vote Republican,” Trump said Thursday.

The real threat to America comes not from the caravan but from Trump’s assault on our democratic norms. He has declared a “national emergency” where none exists. He has talked of sending as many as 15,000 troops to the border — more than we have in Afghanistan or Iraq — even though they are not needed and have no authority to arrest anyone. He has even said that the troops would be expected to shoot people throwing rocks — a violation of the laws of war. The Pentagon is calling this Operation Faithful Patriot. Operation Political Stunt is more like it.

Trump is politicizing the military, leading old soldiers to cry out in protest. Retired Gen. Martin Dempsey, former chairman of the Joint Chiefs of Staff, tweeted, “A wasteful deployment of over-stretched Soldiers and Marines would be made much worse if they use force disproportional to the threat they face. They won’t.” Former defense secretary Chuck Hagel, a Vietnam veteran, said that Trump is using our troops as “political pawns” and that this is “really wrong.”

Also wrong is Trump’s assault on the Constitution. He claims to appoint judges with a commitment to the “original intent” of the Constitution. Well, nothing could be clearer than the language of the 14th Amendment: “All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside.” Yet Trump pretends that somehow by executive order he could deny citizenship to children born here if their parents aren’t citizens or possibly permanent residents.

Why Trump would try to do this is unclear save for his unrelenting animus against immigrants who come from “shithole countries” rather than from majority-white countries such as Germany (like his grandparents) or Slovenia (like his wife). There is no problem with too many people claiming U.S. citizenship. It’s not as if America is overcrowded: The United States has 35.6 people per square kilometer, compared to 272 people per square kilometer in the United Kingdom. And it’s not as if immigrants are dragging us down economically — Trump himself brags about how our economy is the greatest ever. Like the “crisis” of illegal immigration, the “crisis” of birthright citizenship is concocted out of whole cloth by nativists — and that appears to be precisely the constituency that Trump is pandering to.

It is not shocking that Trump would stoop so low. With him, there is no bottom. What is shocking, if no longer entirely surprising, is that the Republican Party would so readily follow him into the gutter. The prominent Republicans denouncing his hate-mongering are mostly those such as Sen. Jeff Flake (Ariz.), Sen. Bob Corker (Tenn.) and Gov. John Kasich (Ohio) who are not seeking reelection. The rest of the GOP is complicit in this disgraceful demagoguery. Republicans who do not denounce Trump’s racist tactics — and even imitate them — will never escape the stench of this year’s campaign as long as they live.