"You guys still sure you're American citizens? OK, we'll check back in around 20 minutes."
Due to a treaty that prevents building in certain areas near the border, the USA figured they had a bit of buffer room around where they actually built the fence, so some Americans got to watch in horror as their country built a huge "KEEP OUT" wall that left them on the outside, like the dick in every horror movie who locks the door while one guy is still outside getting swarmed by zombies. So, every day, Americans living in America have to cross the American border fence to enter America.
And even that doesn't really convey the insanity of it; one farmer complains that he has to cross the border every time he travels between his field and his barn. At one point, it even cuts through the middle of a college campus in Texas. So students have to allow time to clear border security while running from one lecture to another.
Here we can see the Border Patrol watching over the border between the United States and the United States.