Illegal immigration has become a heads-we-win / tails-you-lose proposition in this country. If the supporters of amnesty and open borders could get that codified into law, they would. Since they can't, they support comprehensive illegal immigration reform, with the idea being that the amnesty will occur, but they'll stall and slow-walk the security measures into oblivion. Since the people are onto that ploy and have demanded security first, the latest tactic is just to refuse to enforce the law. We can pass a bill that says we're putting a fence on our southern border, but we can't get the fence built. We can catch illegal aliens, but then ICE just releases them. Meanwhile, both parties talk about how important securing the border is, even as they deliberately take steps to make sure it never gets secured.
Why does this happen? Democrats believe, correctly, that illegal aliens would vote heavily Democratic if they become American citizens. So, the more illegal aliens that become American citizens, the more votes Democrats get. Many establishment Republicans foolishly believe that they need to be soft on illegal aliens to bring in more Hispanic voters. How bringing in millions of new votes for the other party -- so you can lose by a smaller margin with a block of voters who are already here -- makes sense as a winning electoral strategy is hard to figure. Additionally, both parties, but particularly the Republicans, have been influenced by sleazy businessmen who want to benefit from cheap illegal labor, while foisting all the costs on the rest of society.
This is why the problem doesn't get solved. The reality is that if the people in D.C. actually want to put an end to illegal immigration, they could do it within a year or two without resorting to the open borders and amnesty crowd's favorite imaginary bugaboo: rounding up millions of people, one by one, and deporting them.
How do we do it?