OAKLAND, Calif. — Twitter said on Friday that it had permanently banned President Trump from its service “due to the risk of further incitement of violence,” effectively cutting him off from his favorite megaphone for reaching the public and capping a series of actions by mainstream sites to limit his online reach.
Twitter said in a blog post that Mr. Trump’s personal @realDonaldTrump account, which has more than 88 million followers, would be shut down immediately. The company said two tweets that Mr. Trump had posted on Friday — one calling his supporters “patriots” and another saying he would not go to the presidential inauguration on Jan. 20 — violated its rules against glorifying violence.
The tweets “were highly likely to encourage and inspire people to replicate the criminal acts that took place at the U.S. Capitol on Jan. 6, 2021,” Twitter said, referring to the storming of the Capitol by a mob of Trump loyalists.
Within minutes, Mr. Trump’s account on Twitter was no longer accessible. His posts were replaced with a label: “Account suspended.”
Mr. Trump tried to evade the ban late Friday by using the @POTUS Twitter account, which belongs to sitting U.S. presidents, as well as other accounts to lash out at the company. But almost all of his messages were almost immediately removed by Twitter. The company forbids users to try avoiding a suspension with secondary accounts.
The moves were a forceful repudiation by Twitter of Mr. Trump, who had used the platform to build his base and spread his messages, which were often filled with falsehoods and threats. Mr. Trump regularly tweeted dozens of times a day, sending flurries of messages in the early morning or late evening. In his posts, he gave his live reactions to television news programs, boosted supporters and attacked his perceived enemies.
“Twitter’s permanent suspension of Trump’s Twitter account is long overdue,” said Shannon McGregor, a senior researcher at the University of North Carolina at Chapel Hill. “This is the key de-platforming for Trump. The inability to tweet cuts off his direct access to the press — and, by extension, the public.”
In a statement late Friday, Mr. Trump said Twitter was trying to silence him. He said he was negotiating with other sites and promised a “big announcement soon,” adding that he was looking at building “our own platform.”
“Twitter is not about FREE SPEECH,” Mr. Trump said. “They are all about promoting a Radical Left platform where some of the most vicious people in the world are allowed to speak freely.”
A day earlier, Facebook had barred Mr. Trump for the rest of his term, and other digital platforms — including Snapchat, YouTube, Twitch and Reddit — also recently limited Mr. Trump on their services.
The actions were a stark illustration of the power of the social media companies and how they could act almost unilaterally when they chose. For years, Twitter, Facebook and other platforms had positioned themselves as defenders of free speech and had said the posts of world leaders like Mr. Trump should be allowed because they were newsworthy. The companies had rejected touching his account, even after they were assailed for allowing misinformation and falsehoods to flow.
Twitter decided to permanently ban Mr. Trump as it faced pressure from lawmakers, its own employees and many others, including Michelle Obama. Other politicians and world leaders also have posted incendiary tweets, raising questions of whether Twitter had started down a slippery slope and would have to take down other accounts.
On Friday, the company also permanently banned the accounts of several prominent Trump supporters who used the platform to spread conspiracy theories, including the lawyer Sidney Powell and President Trump’s former national security adviser Michael T. Flynn. Rush Limbaugh, the conservative talk show host, also appeared to deactivate his account.
Donald Trump Jr., Mr. Trump’s son, called Twitter’s move against his father “absolute insanity” and said the tech companies were overreaching. “We are living Orwell’s 1984,” he tweeted.
“It is now time for Congress to repeal Section 230 and put Big Tech on the same legal footing as every other company in America,” Senator Lindsey Graham of South Carolina said on Friday.
Mr. Trump had repeatedly told allies who raised the possibility that social media firms would bar him, “They’ll never ban me.”
In the White House, there was an extensive process for drafting official tweets. But at night and early in the morning, Mr. Trump composed his own tweets on his iPhone, often to the chagrin of advisers and Republican lawmakers who then spent hours or days dealing with the fallout.
“Without the tweets, I wouldn’t be here,” Mr. Trump told The Financial Times in April 2017.
In a meeting at the White House last year, Brad Parscale, Mr. Trump’s campaign manager at the time, suggested that the president move over to Parler, an alternative social media site that has become popular with right-wing users. But Jared Kushner, the president’s son-in-law and senior adviser, shot down the idea later, sharing Mr. Trump’s confidence that Twitter wouldn’t act, and it never happened, according to a person briefed on what took place.
While the White House still has official Twitter accounts like @POTUS and @WhiteHouse until the inauguration, Twitter has said it will facilitate the transfer of those accounts to the incoming Biden administration. Before the mob attack on Wednesday, Jack Dorsey, Twitter’s chief executive, was involved in discussions about transferring those accounts, a person familiar with the discussions said.
The pushback against Mr. Trump online began on Wednesday after his loyalists, urged on by the president, breached the Capitol building. In the aftermath, Twitter temporarily locked Mr. Trump’s account, followed by Facebook. At the time, Twitter said the risks of keeping his commentary live on its site had become too high.
The company said Mr. Trump could return to its platform if he deleted several tweets that contained falsehoods about the election or calls for violence, which violated its policies. One of the tweets was a video that Mr. Trump had posted after the police pushed the mob back where he told his supporters: “We love you. You’re very special.”
After Mr. Trump took those posts down, he was reinstated to the site on Thursday. Late on Thursday, he issued a conciliatory message, saying he was outraged by the violence and would facilitate a peaceful transition of power.
But Mr. Trump tweeted on Friday that his supporters were “American Patriots” who would possess a “GIANT VOICE long into the future.” He also said he would not attend the inauguration on Jan. 20.
Twitter said those messages appeared to condone Wednesday’s violence and were likely to stoke further violence. It added that the one about the inauguration offered the date as a target for attack.
“Plans for future armed protests have already begun proliferating on and off Twitter, including a proposed secondary attack on the U.S. Capitol and state capitol buildings on Jan. 17, 2021,” Twitter said.
Inside Twitter, employees and executives have debated how to treat Mr. Trump’s account. Mr. Dorsey has been vacationing on an island in French Polynesia this week, but called in to meetings, three people with knowledge of his location said. On Thursday, he sent an email to employees saying it was important for Twitter to remain consistent with its policies, including its policy of allowing a user to return after a temporary suspension, according to one person who received the email.
Hundreds of employees soon signed a petition asking the company to immediately remove Mr. Trump’s account, three people familiar with the petition said. The petition was reported earlier by The Washington Post.
On Friday, Twitter held a meeting with employees, two people with knowledge of the event said. At the meeting, workers pressed executives on why they had not permanently barred Mr. Trump from the platform.
Mr. Dorsey and other managers, such as Vijaya Gadde, Twitter’s head of legal and safety, said the company wanted to be consistent with its policies, which state that users can tweet again if they have deleted the messages that violated its rules.
But Mr. Dorsey also said he had “drawn a line in the sand” that the president could not cross for fear of losing his account privileges, the people with knowledge of the event said. Mr. Dorsey said Twitter would follow through on a ban if Mr. Trump crossed that line.
Emerson Brooking, a senior fellow at the Atlantic Council’s Digital Forensic Research Lab, said taking down Mr. Trump’s Twitter account now was, in some ways, too late because the president had already spread so many conspiracy theories on the platform over the past few years.
“Removing Trump from Twitter does not fix our politics or bring millions of Americans back to reality,” Mr. Brooking said. “But it does make it significantly harder for disinformation to enter the mainstream. And it makes it harder for Trump to reach his followers.”
Beyond muting Mr. Trump’s biggest megaphone, Twitter’s decision could create headaches for the Trump administration when it comes to complying with the Presidential Records Act of 1978, which requires the preservation of presidential materials and communications.
Maggie Haberman, Katie Rosman and Maggie Astor contributed reporting.