It is entirely stoppable, given Americans have the will.
Didn’t they just report that immigration is at a standstill because as many Mexicans have been going home as arriving?
Americans have the will. But, as they say in economics, there is a "structural" problem--the government. And the government's problem is what economists call "the agency problem." A majority of those in government (our agents) are more concerned about the perks of the position and staying in office than the welfare of the country as a whole.