In her 75-page ruling, U.S. District Court Judge Naomi Buchwald, a Clinton appointee, had suggested that Trump mute rather than block some of his critics. But it could affect the conversation that erupts among supporters and opponents in the replies beneath his tweets.
"This is a great precedent we have set for politicians that decide to use social media as a town hall to be held accountable to the rules of the First Amendment", Gu said.
Blocking the complainants from this public space "based on their political speech constitutes discrimination that violates the First Amendment", wrote the judge. But blocking someone also works in the other direction: if Trumpblocks another user, that user can't see Trump's tweets and (as a consequence) can't reply to them.
Twitter's responsibility in policing the public forum was not mentioned in Buchwald's ruling, creating a giant question mark over what specifics should be implemented going forward.
Justice Department attorneys argued that the account was personal and therefore immune to those claims. But, as President, Trump frequently uses it to make official announcements.
Trump, with more than 52 million followers, is the most followed world leader on the micro-blogging site. Rex Tillerson learned he'd been fired from his job as Secretary of State by a tweet from this account, for example.
When Gu was blocked, he said that he didn't feel pride like some Twitter users do when they are blocked.
But being able to comment on a tweet requires following the president - and blocking someone means he or she can not jump in with their thoughts.
"I suedthe president, and I won", Ms. Buckwalter Poza said on Twitter. Among them was Rebecca Buckwalter, a writer and political consultant who was blocked in June after responding to Trump's tweet that he would have had "ZERO chance winning WH" if he had relied on the "Fake News".
The lawsuit against Mr Trump and other White House officials stems from his decision to bar several online critics.
"This case requires us to consider whether a public official may, consistent with the First Amendment, "block" a person from his Twitter account in response to the political views that person has expressed, and whether the analysis differs because that public official is the President of the United States", writes Buchwald.
"The answer to both questions is no".
Digital rights advocates applauded the ruling as a victory for First Amendment rights on social media.
Trump blocked co-plaintiff Holly Figueroa O'Reilly a year ago after she tweeted a gif of Pope Francis glancing at Trump with (what seems) like a disapproving expression.
Trump can, however, "mute" users, meaning he would not see their tweets while they could still respond to his.
While neither Trump nor Scavino are allowed to block users, Buchwald did not order them to unblock users.
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