On Last Week Tonight's last episode of the year on Sunday, John Oliver walked through the very, very rigorous vetting process that Syrian refugees go through — debunking the idea that a terrorist could easily infiltrate the US by posing as a refugee.

Oliver explained:

If you're a refugee, first you apply through the United Nations High Commissioner for Refugees, which collects documents and performs interviews. Incidentally, less than 1 percent of refugees worldwide end up being recommended for resettlement. But if you're one of them, you might then be referred to the State Department to begin the vetting process.

At this point, more information is collected. You would be put through additional screenings by the National Counterterrorism Center, the FBI, and the Department of Homeland Security. And if you're a Syrian refugee, you'll get an additional layer of screening called the Syria enhanced review, which may include a further check by a special part of Homeland Security, the USCIS fraud detection, and national security directors.

And don't relax yet 'cause we've barely even started. Then you finally get an interview with USCIS officers, and you'll also be fingerprinted so your prints can be run through the biometric databases of the FBI, Department of Homeland Security, and the Department of Defense. And if you make it through all that, you'll then have health screenings — which, let's face it, may not go too well for you, because you may have given yourself a stroke going through this process so far. But if everything comes back clear, you'll be enrolled in cultural orientation classes — all while your information continues to be checked recurrently against terrorist databases to make sure that no new information comes in that wasn't caught before.

All of that has to happen before you get near a plane. This process typically takes 18 to 24 months once you've been referred by the UN to the United States. This is the most rigorous vetting anyone has to face before entering this country. No terrorist in their right mind would choose this path when the visa process requires far less effort.