Mark Collett posted a screenshot of a Breitbart.com story citing opinion in Italy on immigration, where the new government recently refused to admit a vessel carrying African migrants. Collett is a self-described admirer of Adolf Hitler and is active in the digital "alt-right."
King retweeted the post and added: "'Europe is waking up ... Will America ... in time?"
King has stirred controversy with previous anti-immigrant comments such as a tweet last year that said, "We can't restore our civilization with somebody else's babies."
His office hasn't immediately responded to a message seeking comment.
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