Trump is a salesman and a scammer. Talking about the wall's efficiency is meaningless because there will never be one, at least not as Trump supporters imagine it. At the very best, the government may deliver some half-assed construction to deal with voters who are still expecting a big-ass wall to be erected all across the border and this will be it.
But this was never about immigration, it is about the angry and scared people who used to be middle class and are trying to cope with being poor and left behind. It is about the people who got scammed into believing they would be middle class forever and are now getting scammed into supporting a populist leader who wasn't even paying his own workers when he was a businessman. I wonder what will happen when Trump leaves office and all these fanatics realize they are still poor, forgotten and hooked into opiates.