By Georgia Wells, Ian Talley and Jeff Horwitz

In the weeks since the Nov. 8 election, an online provocateur and white nationalist named Tim Gionet posted hours of live-stream videos to social media in which he repeatedly warned of rioting or worse if the results weren't overturned. "Trump or war!" he said in a video posted on Tuesday.

The next day, Mr. Gionet live-streamed from inside Speaker of the House Nancy Pelosi's office as a mob ransacked the U.S. Capitol.

Mr. Gionet was among a collection of right-wing and extremist personalities who loudly rallied their online followings to contest the election results, through violence if necessary, according to researchers and analysts who study extremism and disinformation, as well as posts reviewed by The Wall Street Journal. Many of them used the reach of mainstream social-media platforms such as Facebook Inc. and Twitter Inc. but increasingly also turned to niche sites with either fewer rules around the type of content that can be posted and/or where the communications can be encrypted, and thus inaccessible to law enforcement.

Mr. Gionet, who was previously banned from YouTube and Twitter for abusive behavior, posted his videos to Facebook Inc.'s Instagram service and the streaming platform DLive.

His account had remained active on Facebook, where he mostly refrained from expressing extreme political views, illustrating the patchwork enforcement that has been constructed as platforms reach different and often conflicting decisions about what is acceptable. Late Thursday, Facebook removed Mr. Gionet's profiles from Facebook and Instagram.

Mr. Gionet, who goes by the nickname "Baked Alaska" online, didn't respond to requests for comment.

Unlike other rallies in the past that turned violent, the Capitol riot doesn't appear to have been orchestrated by a central figure or organization, according to researchers and analysts. Instead, they say, these online rabble-rousers fomented anger over the election results for weeks through various channels and platforms.

"It was a bit of a mess," said Megan Squire, a professor of computer science at Elon University who focuses on online extremism. "There were so many groups, it was broken out across numerous platforms, and fewer people were claiming to be in charge."

Yet it was hardly unpredictable.

The SITE Intelligence Group, which monitors extremist groups, sent more than two dozen alerts between Dec. 23 and Jan. 7 noting the rising risk of violence related to the coming gathering.

Robert Evans, who specializes in far-right extremism for the research group Bellingcat, predicted an attempt on the Capitol in a post Monday on Bellingcat's website.

"It was planned by a distributed network of extremists for months, and in some ways for years," said Mr. Evans, who has advised federal law enforcement on the growing extremist movement in the U.S.

Mr. Evans, pointing to multiple social media and chat room sites, said symbols used by rioters captured in videos and photos of Wednesday's attack identified the ideology of conspiracy theories promoted by far-right extremist groups, especially QAnon, a loosely organized community that believes a cabal of Satan-worshipping pedophiles is trying to undermine Mr. Trump. A noose in one protester's hand is likely to represent the white-supremacist slogan "The Day of the Rope," he said.

Federal authorities said Thursday they plan to charge dozens of people for their roles in the riots, in part by combing through social-media activity in search of clues.

Other platforms where Wednesday's rally was widely promoted include Discord, Parler and Gab, each of which puts fewer restrictions on posts than Facebook and Twitter, which forbid incitements to violence and in recent months have taken steps to limit false claims about the election.

A spokeswoman for Discord said the app has strict rules against hate and violence of any kind, including the use of Discord to support or organize around violent extremism.

In early July, Facebook booted groups advocating for civil war, and in August and early September, Facebook targeted militia groups, conspiracy groups such as QAnon, and the far-right extremist group Proud Boys.

Facebook in the past had banned some members of these groups, but this time took a more aggressive approach. "Facebook disrupted their networks, " Dr. Squire said.

Facebook, though, remained a key hub for awareness of the coming rally and discussion of possible actions to contest the election result.

While Facebook after the election banned the more than 300,000-member "Stop the Steal" group, it allowed the organization behind it--"Women for America First"--to continue promoting events disputing the legitimacy of the election and calling for efforts to overturn it.

That group's rally was where Mr. Trump on Wednesday told attendees they should "walk down to the Capitol" and warned "you will never take back our country with weakness." Protesters rushed the Capitol shortly thereafter.

In the day before the mob attacked the Capitol, many public and private pro-Trump groups across Facebook were warning of a looming "civil war," according to an analysis by Avaaz, a left-leaning human-rights group.

One video circulating on Facebook, posted on Jan. 3 and viewed almost 45,000 times, explained to viewers how they could go and buy pepper spray, carry a knife or pistol and briefed watchers on the laws around conceal and carry, said Fadi Quran, campaign director at Avaaz. Facebook removed the video after Avaaz alerted them to it.

Ahead of the rally, the administrators of a private Facebook group called the 2020 Civil War--which has grown to 1,400 members after organizers launched it in September to discuss fighting in and surviving coming unrest --advised members who traveled to Washington, D.C., on where to meet up with like-minded Trump supporters and suggested that they bring concealed weapons with them.

"They just do not have the moderation tools to deal with this stuff at scale and when it matters," said Claire Wardle, co-founder and U.S. director of First Draft News. "A lot of this stuff has been tolerated for years and years--it's not going to stop today."

After the election, these groups coalesced around the hashtag and movement "Stop the Steal," which Mr. Trump promoted along with his false claims that the election had been rigged. They began hosting events in the capitals of the states whose election results they hoped to contest, Dr. Squire said. These in-person events included appearances from white nationalist Nick Fuentes and Mr. Gionet, who appeared together at an event in Arizona in November, and conspiracy theorist Alex Jones, who joined Mr. Fuentes at a similar event in Georgia. They continued pushing "Stop the Steal" ideas, until they converged in Washington on Wednesday with the other rioters.

"I think they understood that their job was to overwhelm the Capitol and stop the vote," Dr. Squire said. "They didn't need central planning."

The groups are now gearing up for their next event: Jan. 17, the first anniversary of the pro-gun rally in Richmond, Va., and a few days before the inauguration. Dr. Squire said she has found fliers promoting this event on all the major platforms.

Deepa Seetharaman

and Erin Ailworth contributed to this article.

Write to Georgia Wells at Georgia.Wells@wsj.com, Ian Talley at ian.talley@wsj.com and Jeff Horwitz at Jeff.Horwitz@wsj.com

(END) Dow Jones Newswires

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