Trump blocked specific users from posting / commenting on his twitter account. He was censoring those who disagreed with him when he blocked them. In May 2018, a federal court determined that it was UNCONSTITUTIONAL for POTUS to block commenters from his official POTUS twitter. The ruling was appealed in June, but I don't know the status.  
http://www.cnbc.com/2018/05/23/trump-cant-block-twitter-followers-federal-judge-says.html
http://www.npr.org/sections/thetwo-way/2018/06/05/617029134/white-house-appeals-ruling-that-president-cant-block-twitter-followers  
"the president's account, which has more than 52 million followers, is a "public forum" and that blocking users is a violation of the First Amendment's free speech guarantee. ... No government official — including the President — is above the law,' she wrote, 'and all government officials are presumed to follow the law as has been declared.' "
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Trump tweeted earlier today that: “Social Media is totally discriminating against Republican/Conservative voices. Speaking loudly and clearly for the Trump Administration, we won’t let that happen.”  
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Apparently, Trump thinks that HE is above the law and he will pursue HIS appeal so that he can censor opposition comments on twitter but OTHERS must NOT censor hate speech, personal attacks, or incitement to violence.

I get that the potus Twitter account is a public forum but if the 1st amendment reigns supreme on the twitterspheere. The should ring true for anyone who posts on Twitter. They should be allowed to say what ever they want, Russians included.

"Apparently, Trump thinks that HE is above the law and he will pursue HIS appeal so that he can censor opposition comments on twitter but OTHERS must NOT censor hate speech, personal attacks, or incitement to violence. "  
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I should have added "... incitement to violence IF IT COMES FROM TRUMP FRIENDS, SUPPORTERS, AND ADVOCATES." If twitter censors accounts of those opposed to Trump, Trump would, NO DOUBT, approve.

The shareholders of Twitter have the final say in what can and can not be said on Twitter and by who, and the share holders of Twitter are not all Americans.

If Twitter blocked the accounts of the users who Trump blocked. There wouldn't be anything they could do about it, free speech wouldn't matter, Twitter is the owner of Twitter.