Notice it is 2019 and not 2017. He had two years to build a wall. He had little interest in the wall for those two years. There's been another election. His side lost the House. The House holds the purse strings.
The whole promise was that Mexico would pay for a wall on the southern border. It matters when you omit the other part of the promise.
Trump on Twitter
"....I do have a plan on the Shutdown. But to understand that plan you would have to understand the fact that I won the election, and I promised safety and security for the American people. Part of that promise was a Wall at the Southern Border. Elections have consequences!
8:07 AM - 12 Jan 2019"