John Oliver’s Last Week Tonight episode about Republican frontrunner Donald Trump has become the host’s most popular to date. After being up on YouTube for about a week and a half, the video has already been viewed over 20 million times. His next-most-popular video has been on the site for over a year and has about 12 million.

In the episode, Oliver discussed the power of the Trump name and how it’s often associated with wealth and success. “The very name Trump is the cornerstone of his brand,” he said. However, Last Week Tonight discovered that one of Trump’s ancestors had changed the name from “Drumpf,” which Oliver says “is much less magical.”

The hashtag #MakeDonaldDrumpfAgain took off after the episode aired and, according to the New York Times, a Chrome extension that changes all mentions of Donald Trump to “Donald Drumpf” has already been downloaded over 433,000 times.

Perhaps the most notable thing to come out of the episode was a “Make Donald Drumpf Again” hat modeled after Trump’s ubiquitous baseball caps with his slogan, “Make America Great Again.” The product is described on HBO’s website as “A hat, specially designed to be worn on the head, as a reminder of the real Donald Drumpf,” along with the added fact that “All hats are being sold at cost, because we know nothing would irritate him more than someone choosing not to make a profit.” They sold out in just over a week due to “unexpected ludicrous demand.”

This was an unexpected episode coming from John Oliver considering comments he’s made in the past expressing his disinterest in covering Trump on his show. But as he explains in the segment, “At this point, Mr. Trump is America’s back mole. It may have seemed harmless a year ago, but now it’s gotten frighteningly bigger, and it’s no longer wise to ignore it.”

Trump is currently leading the Republican party with 458 delegates having won 15 primaries out of a total 23.