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President Donald Trump's frequent Twitter posts about politics, policy, and his personal life continue to catch the praise and ire of many. And just like any user of the social media site, Trump doesn't have an obligation to address any of the replies he may take issue with. But does he have a right to block people he disagrees with?

Last week, in response to a tweet of Trump's weekly address, user @joepabike tweeted at the president: “Greetings from Pittsburgh, Sir.” He then asked: “Why didn’t you attend your #PittsburghNotParis rally in DC, Sir? #fakeleader." Trump proceeded to block this user.

Yesterday, three free speech advocates from the Knight First Amendment Institute at Columbia University sent an open letter to President Trump. The say the president cannot block Twitter users, arguing that Trump's Twitter feed is a forum for public policy that the government cannot exclude people from. On Tuesday, White House Press Secretary Sean Spicer even said that the president's tweets should be taken as official statements.

Katie Fallow, a senior attorney at the Knight First Amendment Institute and a former senior staff attorney at the ACLU, explains why she and her colleagues believe the president's move to block Twitter users violates the Constitution.