The community is notoriously difficult to manage. Its top moderator team has turned over at least four times, according to Mr. Huffman. (This usually happened because the community revolted, as in one instance in which a lead moderator wrote that he believed he could get away with raping undocumented immigrants.) Moderators also suspend and bar members more frequently than do moderators of any other section of the site.

Still, by early 2016, its content so regularly took over Reddit’s most popular lists that the company decided to change its algorithm to make it harder for posts from groups like The_Donald to reach prominence, according to employees. When he announced the change, Mr. Huffman said it had been in the works for a while, but also that Reddit was being undermined by The_Donald’s attempts “to dominate the conversation.”

The community’s power soon reached beyond Reddit. Mr. Trump tweeted out memes and videos that originated on The_Donald and in July he participated in a popular Reddit “Ask Me Anything” discussion, after his team communicated with the moderators.

This would make little sense if The_Donald were all memes and derision. But according to Reddit, The_Donald’s moderators — nearly 50 far-flung volunteers — deftly managed to channel action out of the chaos. They hosted an extensive and at times informative Wiki about Mr. Trump’s policy proposals and instructed supporters how to help with the campaign. Members often suggested strategies for arguing persuasively against opponents.

Perhaps most important, members organized an effort to comb through the Democratic National Committee emails released by WikiLeaks over the summer. In order to interpret and disseminate these documents, The_Donald relied on a network of subscribers it (adoringly?) named “weaponized autists.” Of particular fixation were emails from the Clinton campaign chairman, John Podesta. In a debate in October, Mr. Trump said to Mrs. Clinton, “John Podesta said some horrible things about you.”

There is no way to know how much all this online activism made a difference on Election Day. But there were many discussions of how The_Donald’s hundreds of thousands of members could persuade their friends on Facebook and elsewhere to get out to vote. And, after all, they spent months discussing Nov. 8 on Reddit; it’s hard to imagine they didn’t spend a few minutes in a voting booth.

But now that Mr. Trump is the president-elect, what will happen to The_Donald? What will the centipedes do when the Trump administration becomes the establishment, engaging with lobbyists and compromising on ideals, and all of the typically “Washington” behaviors they despise?