It absolutely makes sense for Trump to insist on getting funding for The Wall, because he knows that his supporters have negative feelings about Central and South Americans, particularly Mexicans... that's why he promised The Wall in the first place... he knew that there was a large segment of Americans who would really love the idea of a large "Mexicans Keep Out!" monument.I think it makes sense for trump to insist on his wall, cause that was his main thing when he was in the primaries. Of course mexico wont pay for it, but it will be funny to see a few tens of billion dollars used for a border wall.
If it is to deter without threat of manual use of force, it would have to be seriously tall and sturdy.
That said, even if would get built, the immigrants could just use the sea route. Though i suppose they would have to land on red states.
As far as actually keeping people out... people will continue to dig tunnels under the wall, and use the numerous already existing tunnels so The Wall is useless... except as a symbol... but that's OK, because that's the real reason people want it... to let those Mexicans know that this is a white, English speaking country and we want to keep it that way... so we don't want them here.