World leaders, including Trump -who has violated Twitter's policy on numerous occasions- are exempted from ban. The exemption will lift in Jan.
However, though it all, Twitter did not ban Trump from Twitter; it did not even suspend his account. The company wrote a policy wherein “world leaders, candidates, and public officials” are exempted from some of its rules, which are grounds for suspension or ban. Incitement to violence, hate speech, targeted harassment are offenses that would get others removed from Twitter but were acceptable from Trump and other politicians. Now, Trump is two months away from leaving office and will be a private citizen, whose account can be banned by Twitter.
The Atlantic noted that "Twitter has been extremely reluctant and somewhat vague about its decisions to outright ban famous people in the past. It has been exceptionally unwilling to implement bans when they can appear to lend credence to the right-wing's famous narrative about being “censored” by Big Tech."
The Atlantic reached out to Twitter to ask whether they could suspend Trump's account, but Twitter would not tell them whether Trump would get suspended or banned if he continued to tweet election-related and other misinformation after Jan. 20, 2021. The company would not say who would be empowered to make the call or how much detail the company would provide about its reasoning if it did so.
Kate Starbird, a researcher at the University of Washington who has studied the spread of disinformation, told the Atlantic that "she didn’t think Twitter would deactivate Trump’s account and didn’t have an opinion on whether it should, but that it would absolutely have a huge impact if it did." He further said, “Donald Trump has an effect on the ecosystem of Twitter that is massive.” She demonstrated with an anecdote. The systems that she uses to do her research can collect 50 tweets a second. Usually that’s fine. But when her team was collecting data on Twitter mentions of hydroxychloroquine in the spring, it was impossible to keep up. As soon as Trump entered the conversation, 50 tweets a second became only a tiny percentage of the data.