The analogy that I have recently heard to describe the situation is that if you owe the bank a hundred thousand dollars, that is your problem. But if you owe the bank one hundred million dollars, that is the bank's problem.
By allowing illegal aliens to stay in the country for over half their life, the government in effect owns the problem now. Proper enforcement of borders and over-stays and things like e-verify to ensure that all hires are legal, and that all students in all schools are legitimately attending their schools, shifts the burden onto the illegals alone. That kind of enforcement makes it the illegal immgrants problem. and takes the profit out of their illegal activity.
However by cooperating with the illegals until they have built a life in America, the government in effect legitimizes them, and makes them functionally legal.
The fact that the government -and businesses- has been cooperating with the cheaters in order to flood the market with cheap labor, and thereby keep labour costs low and profit margins high makes the government complicit in the illegal acts of the immigrant cheats.
It is not an impossible task to control the border and to control illegal immigration. Just by talking tough, and nothing more, Trump has been able to take a huge chunk out of the flow of illegal immigrants.
That sells well enough to the base and to a majority of Americans who really do want a nation of laws and fairness in the immigration assessment system.
All of a sudden though, even Trump is starting talk like the establishment politicians of the GOP and Dems, and talk with his heart. This is really not compassion talking, is it?. The same people that benefit from a huge pool of cheap workers with no legal rights to be in the country and thereby no avenue to demand rights from their employers, are also the financiers of any politicians election hopes.
Having a 'heart' for this pool of labor really 'hearts' the pockets of these loving politicians.
America's illegal immigration problem would have ended yesterday if their was the political will to end it. Instead the politicians own it.