John Oliver's anti-Donald Trump hat campaign became an unexpected hit

John Oliver "didn't give a damn about Donald Trump" until he had to.

Back in the early days of the election season, in 2015, the host of "Last Week Tonight" didn't think he had to pay much attention to Trump as a presidential candidate, he told Stephen Colbert on Monday night's "Late Show."

But when Trump started taking the lead in winning delegates at the primaries, Oliver's show quickly caught up, dedicating an entire show to decimating the real-estate mogul and crafting a joke hat to sell to viewers.

The hat says "Make Donald Drumpf Again" because long ago Trump's family name was Drumpf.

"The German language is so sonorous, isn't it? Beautiful language," Oliver joked, saying he wanted his audience to see Trump with "fresh eyes."

It took off. Oliver's show sold 35,000 hats (they're currently sold out), though with no profit, since they were priced at cost.

"What's funnier than not making any money on an unexpected, inexplicable hit?" Oliver asked.

The hat even had one celebrity fan.

"Jay Z's people called HBO asking for a hat. I'll say this for starts: buy the hat, Jay Z," Oliver said.

Then discussion turned a little more serious when Colbert asked if a candidate as outrageous as Trump could ever get any traction in England.

"It could happen. It has happened. We had many kings in the past," Oliver replied.

Watch the "Late Show" interview below: