Ok, I have a question which I don't understand. If the wall is intended to keep illegal immigrants out, but allows for people to legally enter the States, why are so many people against it (apart from the argument that the funding can be better spent - which is highly based on opinion of what is defined as 'better')? I feel like there's something I'm missing.
It is symbolic of Middle-America exercising political agency and control. The optics of a 'wall' are triggering to those on the New Left who are more-or-less comfortable with the ongoing demographic displacement and economic marginalisation of middle-America. Media and political elites have spent decades letting these people down gently by instilling the idea that this is a secular trend that politicians have no control over. Those same elites are trying to write articles about how Trump's presidency is already a disaster, that he will be impeached in a year, etc.
Trump will be successful because he will actually do what Bill Clinton said he would attempt in 1992, building the middle-class through higher-wage manufacturing jobs and tightening controls on illegal immigration, but has been left on the shelf by both parties' leadership since then.
The US is undergoing a political re-alignment which will see Trump Republicans hold onto an electoral college majority in the near-to-medium through the White middle-class (including the rank-and-file union Old Left). Increasing numbers of this group will see Trump's 'get-er done', pragmatic patriot-style of governing, delivering tangible quality of life improvements, and on the other hand see the Democrats double-down on their identity politics, and choose the former.
Made mid-five figures betting on Trump victory.