Even if everyone agreed there should be a wall across the entire border it would still take decades to finish. But, we all know most people don't support the wall. It's only popular with some republicans. Everyone else realizes it's pointless regarding immigration and a waste of money.
You'd need someone to hold power for another 20+ years that's not only racist but really stupid to keep going through with it.
There will be no wall across the entire border. This is one of the biggest campaign false promises ever made. It's right up there with "read my lips no new taxes". Of course, if you're a Trump supporter then you're familiar with these kinds of lies considering he also promised something better and cheaper than Obamacare.