Benjamin Franklin wrote under dozens of pseudonyms, and founded western liberal democracy .  The Federalist Papers were anonymous, too.
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Demanding the identity of critics of the state is a desire to intimidate and to silence opposition.  It is an unconstitutional attack on free speech 
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It is the stock-in-trade of authoritarian tyrants and police states the world over, from the Third Reich, to the USSR, to Zimbabwe.  Perhaps you might wish to reflect upon the wisdom of your comment, or perhaps of your choice of friends?
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There is an old saying:
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"Never pick a fight with people who buy ink by the barrel" - Mark Twain
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Trump has needlessly and foolishly picked a fight with the Press.  That is a cardinal error in a democracy.
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Now, having made that mistake, (the political equivalent of choosing to fight a land war in Asia), Trump doesn't want to face up to the consequences of his own acts.
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Is "Cowardly" unfair?
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It doesn't seem  an unfair assessment: He picked this fight himself.