TL;DR - Trump fulfills campaign promise, stock market rallies, liberals upset.
Wasn't his campaign promise that Mexico would pay for the wall?
No. Not at all. This is an example of taking the rhetoric of a negotiator too literally. It's like fact checking the statement hamburgers "a mile high" and claiming it to be a lie.
"I will build a great, great wall on our southern border. And I will have Mexico pay for that wall... Mark my words." - Donald Trump, June 16, 2015.
Usually when people use rhetoric they don't say "mark my words" immediately afterward.
There's not going to be a wall. As a former American who left because he was disgusted with American politics (and in general how full of shit mouthy Americans are), I know this as a certainty.