The wall is brilliant in a way. Not for keeping out Mexicans, even Trump has admitted in speeches that they could get over the wall with a rope and a ladder.
No, it's brilliant in its catchiness and as a trap for opponents. It's easy to chant "Build a Wall" and get everyone cheering along.
Then some liberal, or any sane person, will point out how stupid a wall is. How people can go around it in the water, or climb over it, or tunnel under it.
That's when the trap gets sprung:
"They don't care about border security!"
The Wall is a great manipulative tool that you can use it to make anyone who doesn't want a want a wall look like they don't want security.
No matter how false that narrative is. No matter how many better solutions are proposed.
Oh, and if someone says it's racist you can start to claim they say everything is racist too! Because, after all, it's about border security and national security. Never mind that he only wants a wall to keep Mexicans out, and he's ignoring all the other illegal immigrants that come in through airports.