Max Boot is a senior fellow at the Council on Foreign Relations.

This election year is memorable for many reasons but among the most important is showing Republicans the cost of their infatuation with “alternative” news sources.

The rise of the conservative alternative media can be traced back to the founding of the newspaper Human Events in 1944, Regnery Publishing in 1947 and National Review in 1955. But it did not become a mass phenomenon until the debut of Rush Limbaugh’s national radio show, in 1988, followed in 1996 by the launch of the Fox News Channel and the Drudge Report. Those still remain three of the most popular outlets on the right, but they have been joined by radio hosts such as Mark Levin and Michael Savage, authors such as Ann Coulter and Dinesh D’Souza, and websites such as Breitbart News, TheBlaze, Infowars and Newsmax.

The original impetus for these outlets was to offer a different viewpoint that people could not get from the more liberal TV networks, newspapers and magazines. But soon the alternative media moved from propounding their own analyses to concocting their own “facts,” turning into an incubator of conspiracy theories such as “Hillary Clinton murdered Vince Foster” and “Barack Obama is a Muslim.”

[How much damage could a President Trump do? We can only begin to imagine.]

This might have been dismissed at one time as a fringe phenomenon. But it has moved into the mainstream now that the Republican presidential nominee has turned over his campaign to Stephen Bannon, executive chairman of Breitbart, which has become notorious as part of the white supremacist “alt right.” On Sept. 27, for example, Breitbart ran a vicious anti-Semitic attack on the historian and Post columnist Anne Applebaum. On Sept. 16, the site used a picture of a gorilla to illustrate an article about President Obama.

That Trump would ask Bannon to run his campaign is hardly surprising given that the candidate is so deeply in thrall to the same extremist, conspiratorial worldview. These days it’s hard to know where the alternative media ends and the Trump campaign begins. On Monday, the Drudge Report had on its front page a picture of Danney Williams, an African American man, above the headline, “I am Bill Clinton’s Son!” The link went to a YouTube video of longtime Trump confidant Roger Stone ranting to conspiracy-mongering radio host Alex Jones — and never mind that in 1999 the Drudge Report itself had reported that a paternity test had proven Clinton wasn’t Williams’s father. This is the same Roger Stone who this summer accused the Khans, a Gold Star family, of being agents of the Muslim Brotherhood.

Trump hasn’t embraced these smears — yet. But he has echoed plenty of other craziness peddled by the alternative media.

After he blew up at Alicia Machado, the former Miss Universe who has said that he called her “Miss Piggy” and “Miss Housekeeping,” Trump wrote on Twitter: “Did Crooked Hillary help disgusting (check out sex tape and past) Alicia M become a U.S. citizen so she could use her in the debate?” This echoed prurient claims that Machado was a porn star — assertions that are irrelevant if true but that have been debunked by Snopes.com. Turns out that the porn clips circulating online feature another Latino actress and the “sex tape” is an outtake from a reality TV show. The claim that Clinton somehow engineered Machado’s citizenship has no foundation at all.

[This video of Trump talking to a voter about jobs should worry Republicans]

Also last week: Trump denied that agents of the Russian government hacked the Democratic National Committee (as intelligence briefers reportedly told him with “high confidence”), claimed that unscientific online polls were more legitimate than scientific polls and suggested that Google is deliberately skewing search results to leave out bad news about his opponent.

Such wild assertions are fully in character for a candidate who has spent five years pushing the lie that President Obama was not born in the United States, and has also suggested that Texas Sen. Ted Cruz’s father was involved in the assassination of John F. Kennedy, that global warming is a Chinese hoax (in the first debate, he brazenly denied saying this), that “thousands and thousands” of Muslims in Jersey City, N.J., cheered 9/11, and that vaccines cause autism.

Where might Trump get such nutty ideas? He derides the mainstream media as “disgusting and corrupt,” but heaps praise on the National Enquirer, which he said should have received a Pulitzer Prize, and on Jones, a radio host who has claimed that 9/11 and Sandy Hook were “false flag” operations carried out by the U.S. government. “Your reputation is amazing,” Trump told Jones last year. “I will not let you down.”

You can and should blame Trump for believing so much of the nonsense that is spouted by the alternative media, but the deeper problem is with the outlets themselves. The right wing has created its own echo chamber which is increasingly disconnected from reality. There are millions of Americans who share Trump’s outré beliefs — which helps to explain why his presidential campaign has done better than expected.

But in the long term, the right’s addiction to its own news has become destructive — it promotes the election of tea party absolutists to Congress and the nomination of presidential candidates who have trouble appealing to swing voters. Perhaps it’s just a coincidence but in the 28 years since Limbaugh was syndicated, Republican presidential candidates have won a popular majority only once (2004); in the 28 years before then, Republicans won the popular vote five times (1968, 1972, 1980, 1984, 1988). Whether Trump wins or loses, conservatives need to re-evaluate their infatuation with “alternative” news sources that tell them what they want to hear and join a more mainstream conversation that includes different points of view.