Texas congressman John Cornyn prompted confusion and incredulity with an out-of-context Twitter post quoting the former Italian ruler.
He tweeted on Sunday: “We were the first to assert that the more complicated the forms assumed by civilisation, the more restricted the freedom of the individual must become.”
More than six hours later, after being asked to clarify the post, he said he was warning ”against an overly powerful central government”.
“Since so-called Democratic Socialists have forgotten or never learned the lessons of history, and how their ideology is incompatible with freedom, I guess we have to remind or teach them,” he tweeted.
Twitter users pointed out that Mr Cornyn was attacking socialism by quoting a fascist who ordered the murder of his socialist political opponents.
“I can’t decide if you’re too dumb to understand the quote or just a terrible American,” said one. “The lesson of history is that Mussolini was an enormous liar, and that he slandered progressive forms of government with fear mongering so that he could promote a far-right agenda built on patriotic distraction to enact the most dreadful anti-liberty policies possible.”
Canadian writer Jeet Heer tweeted: “When you consider the number of Democratic Socialists who were jailed and murdered for opposing Mussolini and Hitler, the true obscenity of this tweet becomes glaring.”
Jared Holt, a reporter for Right Wing Watch, wrote: “Senator who quoted Mussolini says he did so to warn against socialism, while neglecting to mention that Mussolini killed off his socialist opponents.”
Mussolini, who ruled Italy between 1922 and 1943, organised armed squads known as Black Shirts to terrorise political opponents.
Mr Cornyn will stand for a fourth term in 2020, and Donald Trump last week endorsed his re-election bid.
“Senator John Cornyn has done an outstanding job for the people of Texas,” the president tweeted.
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies