As supporters of President Donald Trump stormed the Capitol building Wednesday, clashing with police, vandalizing offices and causing mass evacuations of lawmakers and congressional staff, critics accused Facebook and Twitter of allowing Trump to incite violence and assailed them for not suspending his accounts.

“There have been good arguments for private companies to not silence elected officials, but all those arguments are predicated on the protection of constitutional governance,” said Alex Stamos, a former chief security officer at Facebook who now runs the Stanford University Internet Observatory. “Twitter and Facebook have to cut him off.”

Wednesday evening, Twitter locked Trump's account for 12 hours and said it would permanently suspend it, if further tweets violate its rules. After 9 p.m., Facebook said Trump violated its rules and imposed a 24-hour block on his account, meaning he will lose the ability to post on the platform during that time.

Both companies added labels to a post by Trump on Wednesday afternoon criticizing Vice President Mike Pence, who was inside the Capitol building, because he would not object to cementing Joe Biden’s victory in the 2020 presidential election, which Trump has falsely claimed was fraudulent. But the mob on Capitol Hill grew angrier, despite the labels.

“There are no legitimate equities left and labeling won't do it,” Stamos said on Twitter.

Twitter later blocked users from sharing multiple posts by Trump “due to a risk of violence.” In a statement to reporters, Facebook said it prohibits “incitement and calls for violence.” Both companies said they were reviewing content on their sites and could take additional action.

Later on Wednesday, Facebook said it had deleted a video post in which Trump asked his supporters to leave the Capitol, even as he praised their actions and repeated false claims that the election was stolen.

"This is an emergency situation and we are taking appropriate emergency measures, including removing President Trump's video," said Guy Rosen, Facebook's vice president of integrity. "We removed it because on balance we believe it contributes to rather than diminishes the risk of ongoing violence."

Following that action by Facebook, Twitter also removed Trump's video along with at least two other posts that sought to encourage the mob and said it would lock the president’s account for 12 hours. The company said future violations of its policies could result in permanent suspension.

Online extremism experts have said since the election that labeling Trump’s tweets were unlikely to curb the spread of lies and conspiracy theories he often posts. And they warned that it would not be long before his supporters’ online anger would spill into violent reality.

Renee DiResta, who studies disinformation also at the Stanford Internet Observatory, posted a video on Twitter of the mob storming the Capitol “for anyone still wondering whether propaganda and misinformation have an impact. Whether online conspiracy theories matter. If QAnon and related communities were ‘just some people online.’”

The companies also took flak because at least some of the pro-Trump protesters had used their sites to organize activities Wednesday. Buzzfeed News reported that a group called Red State Secession, with more than 7,000 followers on Facebook, called for a revolution and asked members to share addresses and travel routes of “political enemies.”

Christopher Wylie, the data scientist who helped blow the whistle on the Cambridge Analytica-Facebook scandal, blamed the company for the events on Capitol Hill.

“These people were all radicalized on Facebook,” Wylie tweeted. “This event was organized on Facebook. This violence is an inevitable manifestation of the conspiracy, vitriol, and hate fed to people daily on Facebook.”

Protesters on Wednesday used other social media platforms as well, including Gab and Parler, which have attracted a right-wing following because they are less likely than Facebook or Twitter to moderate violent content and disinformation. 

They used the apps to organize their movements in and around the Capitol without encountering police, the New York Times reported. Several users posted about carrying firearms into the building, the Times said, and used the apps to try and locate Pence as news that he would not block certification of the election spread.

Wednesday’s events are all but certain to result in new pressure on Facebook and Twitter to limit the spread of violent content and disinformation on their sites, especially with Democrats set to control both chambers of Congress and the White House. Democratic lawmakers and President-elect Joe Biden have long urged the companies to do more.

If Biden and other Democrats remain dissatisfied, they may seek to force the companies to take action by threatening changes to a 1996 law, known as Section 230, that protects online companies from lawsuits related to third-party content on their site and gives them the power to moderate content as they see fit.

During the election, Biden said social media companies should lose their Section 230 immunity for “propagating falsehoods they know to be false.”