In fact it will increase, once they stop aid to the countries these people come from, making their situation even more desperate and giving them more incentive to head for the comparative safety of the USA, where they might be granted asylum. And then, the increased rate of immigration will be evidence to support the need for a border wall. Hmmm.
If I didn't know better, I'd think it was some sort of long-term scheme. Luckily, I know Trump is more like Heath Ledger's Joker. He just... does things.