Something there is that doesn't love a wall

I've never been a fan of Charles Krauthammer. While I generally dislike conservative columnists, I have a special ire for Krauthammer, who likes to abandon the ethics of his first profession of psychiatry (Harvard, '75) to score cheap points in his current profession by publically "diagnosing" the supposed mental issues of Democratic politicians. In his latest column, Dr. Krauthammer voices his support for a wall on the US-Mexico border:

A barrier is a very simple thing to do. The technology is well tested. The Chinese had success with it, as did Hadrian

They did, eh? How did that work out for them exactly? Wikipedia says:

The Manchus were finally able to cross the Great Wall in 1644, when the gates of Shanhai Pass were opened by Wu Sangui, a corrupt Ming border general, after being bribed. The Manchus quickly seized Beijing, and defeated the remaining Ming resistance, to establish the Qing Dynasty.

So success = the complete overthrow of your country and the establishment of a 300 year dynasty. Gotcha. Well, I guess we have some interesting times ahead of us.