In a postscript to a Saturday email about the latest episode of his web series
"Horace and Pete," the comedian asked fans and readers to "please stop it with voting for Trump."
"It was funny for a little while," he wrote. "But the guy is Hitler. And by that I mean that we are being Germany in the 30s."
C.K. said he was "not advocating for Hillary (Clinton) or Bernie (Sanders)," and that he would indeed welcome a "good smart conservative" to take on the eventual Democratic nominee. But, he added, "Trump is not that. He's an insane bigot. He is dangerous."
A vote for Trump, C.K. argued, would be "a version of national suicide," fueling an empty high like taking "a big hit off of a crack pipe."
The Trump campaign did not immediately respond to a request for comment.
Ohio Gov. John Kasich's name also made an appearance in the email, with the comedian suggesting him as a passable option.
"I mean that guy seems okay," was C.K.'s typically droll assessment. "I don't like any of them myself but if you're that kind of voter please go for a guy like that."
Others have made broadly similar, if less colorful, statements comparing Trump to the genocidal Nazi leader.
Former Mexican President Vicente Fox, a spirited Trump detractor, said
last month that the GOP front-runner "reminds me of Hitler."
Anne Frank's stepsister, in a January essay to mark International Holocaust Remembrance Day, accused
Trump of "acting like another Hitler."
Before that, former New Jersey Gov. Christine Todd Whitman, a Republican, told
CNN's Alisyn Camerota on "New Day" that his plan to halt the immigration of Muslims into the U.S. reminded her of "the kind of rhetoric that allowed Hitler to move forward."
Trump has dismissed such comparisons in the past. When a Philadelphia newspaper made the comparison on its cover last December, Trump, told CNN it was "just another paper going out of business."
When ABC News asked him directly about the comparisons in the context of his plan to ban Muslim travel to the U.S., Trump said he was acting more like Franklin Roosevelt