Congress won't approve it.
And if Elected: What President Trump Could or Couldnt Do
http://www.nytimes.com/2016/06/04/opinion/campaign-stops/and-if-elected-what-president-trump-could-or-couldnt-do.html?_r=1
He could not build the Mexican wall without congressional support. But he could order immigration authorities to deport unauthorized immigrants.
Other things that he CAN legally do as POTUS:
* Bar Muslims from entering the country if he deems them "detrimental to the interests of the United States."
* Slap tariffs on China and other countries, if he declares that they've engaged in "unfair" trade practices.
* Withdraw the United States from the World Trade Organization and NATO, among others.
* Disavow the Paris climate change agreement and withdraw from various climate regulations.
* Direct agencies to use regulations that punish his enemies.
* Direct the Department of Justice to investigate his enemies.
* Crack down on journalism by aggressively enforcing federal secrecy laws.