I wonder whether President Trump didn't shoot himself in the foot on immigration. This Post article has this
graph of apprehensions., showing the big surge in 2019, going back to the apprehensions in the GWBush administration.
The difference between now and then is Bush saw an influx of people aiming to work; Trump is seeing an influx of families claiming refugee status. Because claimed refugees surrender to the first US official they see, Trump's wall is a case of fighting the last war.
But why the surge? I'd blame it on Trump. He came into office having made a big deal out of immigration and his wall. For a while the apprehensions ran about the same level as in the Obama era; Obama having made a big deal out of discouraging immigration as well. But Trump couldn't get support for his wall. Doing what he is so very good at, he generated lots of publicity by attacking
"migrant caravans". That was counter-productive.
By publicizing migrant caravans Tump informed Central American citizens that they didn't have to pay a coyote to smuggle them into the U.S. and incur the risk of dying in the desert; they could travel as a family and claim refugee status. That changes the whole cost-benefit calculus. Trump might as well have advertised--"here's the loophole by which you can live in the U.S. for years, and maybe even become legal."
Now no doubt if Trump had never mentioned immigration people would have learned to take more advantage of the refugee rules, and there would have been a transition to it as well as an increase in net apprehensions. But while Trump's bluster about immigration early in his administration may have discouraged some migrants, it's now created a crisis.