The recent Senate compromise to increase the amount of federal spending on border security by an even larger amount is good news for the overall bill's odds of passing and thus good news for America. But it really makes very little sense and is setting people up for disappointment.
Here's the problem. The Gang of 8 bill sets up a new W Visa program that will give employers a legal pathway for the importation of lower-skilled immigrants. This is a perfectly fine idea. And in principle, a guest-worker program is one of the best things we can do to reduce unauthorized labor migration. Workers would prefer legal status to life in the shadows, and employers would prefer to import workers with legal authorization to work than to hire people off the books. But for this to work, the scale of the W Visa program needs to be roughly equal to the demand for immigrant labor. But while the terms of the W Visa program are designed to ensure that the number of W Visa workers is sharply constrained at times of low labor demand, the commission that's supposed to determine how many W Visas to issue is also required to keep the number below an arbitrary cap that's been determined a priori.
The upshot of this is that if demand for immigrant labor substantially exceeds the number of W Visas the government is allowed to issue, people are going to overstay their visas and work off the books.
Visa overstayers are already a large share of the unauthorized population, and creating a guest-worker program is going to increase the possibility of visa overstaying. You could build the Berlin Wall all across the U.S.–Mexico border and you're not going to solve anything. What you need to do is either increase the number of W Visas (my preference) or increase behind-the-border security or some combination of the two. Personally, I don't really care that a border surge is going to be ineffective. But it can get corrosive in the long term if you promise the voters something your legislation can't deliver. If this bill passes, the immigration-enforcement problem won't be at the border.