America's problem with illegal immigrants has gone unsolved for years, largely because the enforcement methods needed to crack down thoroughly would be Draconian and many of the immigrants fill low-wage gaps in the US economy.
Those same constraints operate in Europe, where the problem is similar in scope. An estimated half-million illegal migrants enter the European Union each year in search of work, mainly from Africa, the Middle East, and the Balkans. Thousands more come seeking political asylum.
An added constraint for the EU is that 15 nations are trying to cope with a vast flow of job-seeking humanity, rather than one.
EU members made a stab at working together to close the door on illegal entrants at their recent summit in Spain. What emerged were a few practical steps and some clear differences over just how tough to get.
Few European leaders would disagree that something has to be done, since immigration is fueling resurgent right-wing politics in their countries. Most of the migrants are Muslims, which adds to concerns about terrorists filtering in.
But a move by Britain and Spain to use the development-aid lever to persuade countries of origin to stem the flow of illegals and take back their deported citizens ran into sharp opposition. France, which has close ties to North African countries such as Morocco and Algeria, insisted on diluting the proposal.
Agreement was reached, however, on strengthened patrols and checks at EU borders. That's no small matter, since identification checks within the union have faded with increased integration, and the EU is weighing expansion. Equally important are steps to unify visa and asylum procedures, so that migrants have no incentive to move around the continent in search of the best deal.
As in the US, however, illegal immigration is not just an enforcement issue. It has an economic facet some industries need the workers. And a humanitarian one the migrants attempting to escape grinding poverty are often mistreated by those who smuggle them in.
A solution, on both sides of the Atlantic, has to include greater efforts to improve economic opportunity in the immigrants' home countries.