"While we must recognize, and are sensitive to, the President's personal First Amendment rights", the court rules, "he can not exercise those rights in a way that infringes the corresponding First Amendment rights of those who have criticized him".
On Wednesday, a judge in NY described the president's Twitter account as a public forum, and said blocking Twitter users for their views violated their right to free speech under the First Amendment of the Constitution. "The answer to both questions is no", she begins her 75-page judgment.
"We respectfully disagree with the court's decision and are considering our next steps", a spokesperson said.
Buchwald's ruling was in response to a First Amendment lawsuit filed against Trump in July by the Knight First Amendment Institute at Columbia University and several Twitter users.
Other media reports said the judge advised Mr Trump to mute critics if he doesn't want to see their activities, but they would be able to see and reply his own tweets. Trump uses the Twitter account for policy and diplomatic announcements as well as to lash out at the media and special counsel Robert Mueller's investigation.
These claimants can not view Trumps tweets, reply to them or see the comments thread underneath them.
Enlarge / These Twitter users are participating in a constitutionally protected public forum, a federal judge has ruled.
It's unclear if Mr Trump will now unblock his critics, but the judge hinted the president could face legal action if he did not comply with the ruling.More news: How Cheeky Princess Charlotte Steals the Show at Royal Wedding
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Buchwald said Trump could opt to mute his critics instead.
Twitter declined to comment on the ruling while the White House and the U.S. Department of Justice, which represents the president in the case, did not immediately comment.
Dissenting view: National Review's David French argues against the ruling, writing that because "Donald Trump's Twitter feed isn't a government-controlled forum", the First Amendment protections for public forums shouldn't apply.
He often eschews the official USA presidential Twitter account, @POTUS, as well as his own White House press office, to make official announcements. "If all goes well, Hollywood will immortalize him as an evildoer who got his comeuppance". "A lot of times with First Amendment cases, the people who were affected by the decision come up with some kind of workaround so they're still in compliance with the First Amendment [while] accomplishing their goals".
However, the Federal District Court for the Southern District of NY found that this was not the case.
The government did not dispute that Mr. Trump blocked people because of those kinds of antagonistic tweets.
If Donald Trump blocks someone, that person loses the opportunity to reply to Trump tweets and have their tweet show up underneath them.
Blocking users on the basis of political speech is a violation of their free-speech rights, the court said.
The Knight Institute hopes that the ruling against Trump will set a precedent for other public officials across the country.