President Donald Trump has lied about almost every major political topic imaginable — unemployment numbers, the crime rate, voter fraud, and even the weather during his inauguration speech. The lies have gotten to be so ridiculous that John Oliver took a break from his usual style of segment to focus on Trump’s deceit.

“Normally, we like to focus this part of the show on complex, depressing policy issues — something fun like CO2 emissions from hearses or space poverty or the proliferation of special-purpose taxing districts, a topic so boring you didn’t even realize we literally already did that exact story last year,” Oliver said on Sunday’s Last Week Tonight. “And we want to keep doing those kind of things. But unfortunately we can’t until we address something even bigger: the concept of reality itself.”

As Oliver explained, one of the fundamental concepts of analyzing policy is agreeing on a very basic set of facts to start from. People can disagree on how to react to some of the facts, although the basic facts should remain largely uncontested. But Trump and his team don’t meet that threshold — not even agreeing on the basic facts, whether the topic is terrorismor former President Barack Obama’s birth certificate.

This can have dangerous consequences, Oliver said: “Real people get hurt when you make policy based on false information. Billions will get spent on a wall that won’t work to prevent a crime wave that isn’t happening, while refugees sit in dangerous situations to prevent Bowling Green–style massacres that never took place.”

So what do we do about it? Oliver had an idea: Given that Trump seems to get so much of his information from cable outlets like Fox News, Oliver will begin buying ads for the DC area on major news outlets — in hopes of catching Trump’s attention as he watches the news. It’s the kind of stunt that Oliver, who once set up a fake church to expose televangelists, has become known for. But this time it’s for a big target: the president of the United States.

“Until we’re shut down,” Oliver said, “we are prepared to educate Donald Trump one by one on topics we’re pretty sure he doesn’t know about.”