Source of illegal immigrants. Nearly 60 percent of illegal immigrants come from Mexico, with which we share a 2,000-mile border. But net migration from Mexico appears to have been zero since the housing bubble burst in 2007.

We don’t know whether it will resume again. But we do know (as we didn’t in the decade after our free-trade agreement) that Mexico’s economy can grow faster than ours, as it is now.

Mexico is becoming a majority-middle-class country, which reduces incentives to emigrate. I predict we’ll never again see Mexican immigration of the magnitude we saw between 1982 and 2007.

If that’s right, it means we won’t see a wave of illegals, as we saw after the 1986 law.