One of the major issues holding up an immigration reform bill is securing the border. Critics warn that if we don't seal off our southern boundary, any bill that allows some illegal immigrants to gain legal status will trigger a surge of new arrivals, like what happened after the 1986 amnesty.
They should put their minds at rest. A reform bill isn't going to increase the population of undocumented foreigners. In fact, it will probably reduce their numbers.
Why? No surge will occur because the conditions are no longer conducive to it. Border enforcement has already made coming here a lot more expensive and uncertain. On top of that, population growth in Mexico has dropped sharply. Jobs in the United States are no longer as easy to get, particularly for unskilled workers. Even an outright "amnesty" would have little effect on the numbers of people coming.
A reform measure, however, would have the effect of sending many of those here back to where they came from. In the old days, a lot of illegal immigrants didn't stay. But as enforcement got tougher, they could no longer leave the U.S. without taking a big risk they couldn't come back. So once they came, they were essentially locked in. With a path to legalization and a reasonable guest-worker program, they would no longer have to remain on this side of the border -- and many would leave.
Being "tough" on illegal immigration has often produced effects that were the opposite of what the advocates expected. A more lenient approach would most likely produce results they don't anticipate -- but would welcome.