Over the last few weeks, posters have used adaptations of the slogan. There was #BidenCrimeFamilly, #BidenCrimeFamilyExposed, #BidenCrimeSyndicate.On Election Day, 17,000 people were posting about #BidenCrimeFamily on Facebook. On Twitter at midday, the slogan was being tweeted 3,500 times an hour.

Trump posted the hashtag on Facebook, this time without any misspelling. Since Facebook wasn’t suppressing the hashtag, there was no need to typosquat around it. That night, Trump used the slogan at a campaign rally in Wisconsin.

Finally, Mr. Trump tweeted the typosquatted hashtag the Friday before Election Day.

A hallmark of a successful disinformation campaign is adaptation — when proponents of the campaign adjust their tactics to get around efforts that journalists, government officials or tech companies have taken to stem its spread. On Oct. 16, campaign operators began adapting to Twitter’s curbs.

Instagram, starting on Oct. 29, suppressed all recent results for every hashtag, showing only a few top posts rather than everything, which had the effect of slowing the spread of #BidenCrimeFamily in the final days of the election.

While users could still tweet the hashtag #BidenCrimeFamily, Twitter stopped showing any results if the hashtag was clicked or searched. This strategy, called de-indexing, is a step short of censorship, and can be a powerful tool in reducing a hashtag’s ability to spread specific disinformation and to become a rallying place for coordinating action. Twitter did not respond to questions about this action.

The more people hear something, the more likely they are to believe it, whether it’s true or not. And false news can spread further and faster than the truth, especially on social media. Mr. Trump seems to understand this.

The asymmetry of attention mirrored that of the Hunter Biden laptop story; while the far-right press was copiously covering it, mainstream news publications were much more careful, largely because most newsrooms were not given access to the documents. The few that were, like The Wall Street Journal, concluded the material wasn’t all that significant.

On Oct. 16, The Daily Beast reported that these Himalaya accounts were a connected network affiliated with Mr. Bannon. Twitter confirmed to Foreign Policy magazine that it had taken down a network of connected accounts pushing Hunter Biden disinformation.

This effort became more urgent when Twitter took the rare step that day of blocking posts with the link to the Post article, explaining that it contained private information and hacked documents, which the company said violated its policies. (Twitter later reversed its decision.) People began tweeting #BidenCrimeFamily, accusing Twitter of censorship, and in some cases linking to another news site, GNews, that had also been pushing Hunter Biden disinformation.

By Monday, there were 21,000 “parleys,” or posts, using the term. It went viral on Gab, another fringe social network popular among the right, and was mentioned on 4chan’s “Politically Incorrect” board (a haven for far-right activists), Facebook, Reddit and thedonald.win, a popular former subreddit that got kicked off Reddit.

People sharing the Post article used the hashtag to collate all the information across social media platforms.

In early October, Rudy Giuliani, the president’s personal lawyer, used the hashtag repeatedly, hinting at what would later be revealed by The Post: that the F.B.I. had seized a computer that purportedly belonged to Hunter Biden.

In this case, the hashtag served two purposes: It made the phrase itself more common, and it amplified The New York Post’s Hunter Biden laptop report.

And Mr. Trump’s typo? It was surely not accidental. That extra “i” circumvented Twitter’s efforts to hide the hashtag in search results. Called #typosquatting, this tactic is often used by trolls and media manipulators to get around the rules of social media platforms.

It’s effective because it’s simple. The hashtag took a complicated issue with legitimate questions about Hunter Biden’s business dealings with Ukraine and China — and reduced it to a slogan that could also be used to spread falsehoods about Joe Biden. (An election-year investigation by Senate Republicans found no evidence of improper influence or wrongdoing by Mr. Biden.)

#BidenCrimeFamily, and the typo, is a crash course in how to rally supporters around a conspiracy theory — while neutering the attempts of social media companies to stop it. With the #StoptheSteal campaign, Mr. Trump is now using this same tactic to sow doubt about the integrity of the election.

In the last month, on Facebook alone, posts with the hashtag had about 277,000 “interactions” like reactions and comments, according to the data analytics tool CrowdTangle — and that’s only on non-private pages. Without the hashtag, the slogan has had more than a million public interactions this month on Facebook.

That moment wasn’t random. #BidenCrimeFamily is part of a yearlong, effective disinformation campaign against Joe Biden — one that was spread by social media, political influencers and the president himself.