Fake news leads eventually to real tragedy. It almost got there Sunday when an idiot reportedly brought a loaded assault rifle into a Washington pizzeria, firing at least one shot, in an attempt to “self-investigate” a preposterous made-up conspiracy theory.

No one was hurt — this time. But the same kind of thing will happen again, thanks to the poison being dispensed by alt-right and white-supremacist propagandists. They concocted “news” stories out of whole cloth during the campaign in an attempt to destroy Hillary Clinton and those closest to her. Is anyone surprised that some people take these paranoid fantasies as gospel truth? I’m not.

President-elect Donald Trump makes matters worse by trumpeting “facts” that are non-factual. To the extent that he shapes the “post-truth” media landscape, he shares responsibility for the consequences.

The made-up story that inspired Sunday’s incident grew out of the hack of Clinton campaign chairman John Podesta’s emails. There were a number of exchanges between Podesta and the owner of Comet Ping Pong, a pizza parlor. Suspicious? Not in the least. Comet is located in the affluent neighborhood that is home to much of the political establishment. And anyone involved in politics knows that campaigns basically run on pizza.

Also, quite a few of Podesta’s hacked emails had to do with food. Apparently, he likes to eat well. How sinister.

Comet Ping Pong customers came out to support the restaurant after a gunman entered it with an assault rifle, firing it at least once. Several other businesses on the block have received other threats as well. (Whitney Shefte/The Washington Post)

In any event, cynics writing on sites such as Facebook, Reddit, Infowars and the Inquisitr spun these innocent facts into a dark, hydra-headed conspiracy involving the alleged trafficking and sexual exploitation of young children. Hidden rooms and secret tunnels were supposedly involved, and no, I am not making this up. Other people made it up, and some gullible readers swallowed it.

Among the believers, apparently, was Edgar Maddison Welch, 28, of Salisbury, N.C., who allegedly walked into Comet Ping Pong waving around a loaded AR-15-style assault rifle. Fortunately, employees and customers were able to flee. Welch allegedly fired at least one shot before surrendering to police, who said he had a second firearm with him in the restaurant and a third in his car. He is charged with assault with a dangerous weapon.

Police said Welch told them he came to the nation’s capital to look into the ridiculous child-trafficking story. He reportedly barged into the pizzeria’s kitchen to search for the entrance to the nonexistent secret tunnels.

Yes, this is all as crazy as it sounds. But the lives of those who happened to drop by Comet Ping Pong or any of the neighboring businesses on a chilly Sunday afternoon were put in real danger by the purveyors of fake news. Morally, those propagandists should be in the dock along with Welch.

Legally, of course, those who make up such stories are protected by the First Amendment. The only way we can shield ourselves from toxic conspiracy theories is to denounce them and disown those individuals and media outlets who spread them. In other words, we can use shame as a disinfectant. Yet next month we will inaugurate as president a man who — in this regard, at least — is without shame.

Trump is the Old Faithful of fake news. He started his late-blooming career in politics by claiming, falsely, that President Obama was not born in the United States. He said that “thousands and thousands” of Muslims in New Jersey cheered the 9/11 attacks, which was not true. He charged, absurdly, that Obama and Clinton were “co-founders” of the Islamic State. He touted a ridiculous National Enquirer story alleging that Sen. Ted Cruz’s father had something to do with the JFK assassination. He repeatedly said, falsely and without evidence, that there was something seriously wrong with Clinton’s health. Apparently stung at having lost the popular vote to Clinton, he claimed that he would have won it if not for widespread “voter fraud” — which simply did not take place, according to officials in the states he cited.

Trump has not, to my knowledge, spoken or tweeted about the pizza “scandal,” although his chosen national security adviser, retired Lt. Gen. Michael T. Flynn, did send a tweet about purported “Sex Crimes w Children.” But the president-elect seems not to realize that it is now in his self-interest to renounce fake news and its creators. Soon, after all, he will be the source of “the official story” about basically everything.

In a post-truth world, how will we know he’s not cooking the economic books? Or that every foreign policy move isn’t designed to further his business interests? Or that his Cabinet doesn’t practice witchcraft?

Real news and “true truth” still matter. As Trump will discover.

Read more from Eugene Robinson’s archive, follow him on Twitter or subscribe to his updates on Facebook. You can also join him Tuesdays at 1 p.m. for a live Q&A.