"Trump says we should be monitoring everyone of the Muslim faith, keeping some kind of registry, maybe even issuing special ID cards," the former Maryland governor said during his remarks at the New Hampshire Democratic Party's annual Jefferson-Jackson dinner. He continued with an unmistakeable Nazi comparison.
"Let me ask you this. Who is next? Catholics? Trade unionists? Artists? We've seen this road before, and it does not lead to a good place," he said.
"Panic and political opportunism are a toxic mix -- a mix that can often precede fascism or the plunging of our republic into a security state," O’Malley added. The audience jeered and booed at his references to Trump.
After the speech, reporters pressed O’Malley on whether he thought Trump himself was a fascist. O’Malley would not say so explicitly, but said the language Trump uses is similar.
"When he pushes things like registries and ID cards based on things like religion, I do believe that is the sort of appeal that historically has often preceded fascism," he said. "We should not think that we are so superior as a nation that we cannot ourselves fall victim to those sorts of appeals."
He added that "we all" should call Trump out on his remarks.
New Hampshire Democratic Party chairman Raymond Buckley said he did not think O'Malley exaggerated the severity of Trump's comments.
"We have seen that elections can go either way," Buckley told ABC News. "The 1 percent chance that Donald Trump is the nominee isn't frightening to us as Democrats, it is frightening to us as Americans."
Trump's campaign did not immediately respond to a request for comment on O'Malley's remarks.
O’Malley has previously made similar comments. Last week, at a press conference in New Hampshire, he called Trump "shameful," and added that he believed the business mogul's appeals were based "wholly in fear” and could plunge the United States "into a security state."