He doesn't talk about it anymore, and neither do other Republicans.
As some answers stated, the wall is under construction,
the wall did not and will not solve any immigration problems, (does n't that sound familiar?)
Trump and the Republicans are seeking additional solutions.
Republicans are realizing Obama was right that "we have a broken immigration system" (December 2015),
and the solution is not to simply build a wall.
Just like they are also realizing that Trump was wrong about the origin of the illegal immigration, and the illegal immigration is not originating in Mexico.