Wouldn't that mean that any talk about the cost of illegals, the benefit of a wall, how many people slip through the border, and crime rate of illegals is worthless? For all we know, only 50 people slip throuh into America a year from crossing the border without documentstion.
Well, we know that border patrol captures tens of thousands of people per month attempting to cross the border illegally. Roughly 400,000 people per year, according to this:
https://www.cbp.gov/newsroom/stats/cbp-enforcement-statistics. Another 200,000 per year are caught trying to enter through a legal passage without authorization (e.g. a vehicle checkpoint). Since we know the amount of people that evade border patrol is greater than zero, then it's just a matter of trying to estimate what percentage of the total people entering the US illegally are getting away with it. If we give BP a lot of credit, and say they capture 90% of illegal aliens, then that still leaves us with 40,000 people per year getting into the nation illegally every year.
Keeping in mind this is after enormous strides in securing the border (which were bipartisan efforts, up until 2015, when it magically became a partisan issue). After Reagan made the amnesty deal, illegal migration surged, with the 90s and 2000s seeing millions of people trying to gain illegal entry each year. As it turns out, rewarding people for illegally coming into the country results in more people doing it.
This isn't going to stop and I estimate it will get many times worse in the coming decades if major climate change predictions pan out and displace millions of people in Central and South America. Desperate people with nothing to lose will begin marching north by the millions and we can only hope Border Patrol is up to the task. It's just too bad Trump can't acknowledge this problem, since he's busied himself denying climate change altogether, though I doubt the Democrat party in its current state would support such a motivation regardless.