After "Make America Great Again," it is perhaps the most common refrain of the Donald Trump campaign.
"I will build a wall!"
And, every time, it's followed by an ironclad guarantee from the candidate:
"And I will make Mexico pay for it."
When asked how, Trump has always been short on details. He cites leverage the U.S. has over Mexico, which needs access to the U.S. market. He has also suggested steep tariffs on Mexican-made goods.