The number of immigrants coming illegally to the United States has been declining for several years. Demographers have repeatedly said as much, and now a report by the Pew Hispanic Center confirms it – illegal migration from Mexico is virtually at a standstill. Last year, about 6.1 million Mexicans were illegally in the country, down from a high of 7 million in 2007.

What accounts for the change after decades of steady increases? A declining birth rate and solid economic growth in Mexico have led fewer people to leave home. On this side of the border, a weak economy has made the U.S. less appealing for job seekers; and tougher border security has made the treacherous journey too expensive and dangerous for most, according to the report.

You might think that this would take some of the pressure off, and that the Republicans and immigration hawks who have spent recent years demanding tougher border security might begin to turn their attention elsewhere. You might think they’d recognize, as many demographers now do, that illegal immigration is going to stay down for a while and that continuing efforts to militarize the border will yield diminishing returns.

The reality is that the border is more secure and less porous than it has been in decades.

The more pressing question now is what to do with the 11 million illegal immigrants from Mexico and elsewhere who are already here. Some Republicans want to redouble efforts to deport them; Mitt Romney has said he hopes they will “self-deport.” But such fantasies of a mass exodus are as unrealistic as the demand for a vacuum-sealed border.

Fixing immigration requires more than an enforcement-only strategy. Lawmakers must undertake a comprehensive approach that includes a path to legalization for those who are here, an agricultural worker program to help growers and farmhands, and strict workplace enforcement to discourage people from coming illegally in the future.