In all democracies, policies that you're running on have to have effects before the next presidential election to assist in the reelection campaign. Ending visa programs will not significantly change demographics until 5-20 years down the line. Unless you think that Stephen Bannon will end democracy before the next election, ending visa programs will not be enough for him.

Also, according to former associates, Bannon is "sinister", "vindictive", and willing to "kill everyone else." Naturally he gravitates to radical solutions over moderate ones. http://www.dailywire.com/news/8441/i-know-trumps-new-campaig...

Obamacare was signed in 2010 and affected the 2010 election even though its implementation was delayed for years.

Voters react to laws that are passed, not only to their effects.