IN the noisy American debate over immigration reform, something important seems to have escaped notice: time, and common-sense decisions by Mexican migrants, have brought us nearly everything immigration reform was supposed to achieve.Migration between Mexico and the United States has returned to a healthy circular pattern: large numbers of Mexicans legally cross northward to work, then return south with confidence that they can repeat the journey the next time. The reason: Even as illegal Mexican migration flattened out in recent years, legal Mexican travel north rose. These migrants have their papers in order. So it’s time to reconsider whether the United States still faces a difficult problem with Mexican immigration. There are many reasons illegal Mexican migration has flattened out. The costs and risks have risen. Demand for labor in the United States has fallen. Growth in Mexico’s labor force has slowed. Yes, the undocumented population in the United States is still about 11.5 million people, about 60 percent of whom are from Mexico, according to the federal Office of Immigration Statistics. But the number is not growing. In fact, data from the Mexican Migration Project, a binational effort by demographers and other researchers, indicates that the rate of undocumented emigration is nearing zero. It peaked at about 55 of every 1,000 Mexican men in 1999; by 2010 it had fallen to 9 per 1,000, a rate not seen since the 1960s. Meanwhile legal migration soared: 517,000 Mexicans entered the United States as legal temporary workers in 2010, while 888,000 entered on business visas and 30,000 arrived as exchange visitors. In 1995 the respective figures were 27,000, 256,000 and 5,000. In other words, Mexicans are coming to the United States to work as eagerly as ever, but they are doing so legally. At the same time, legal permanent Mexican immigration to the United States has exploded, with an average of 160,000 persons entering annually since 2005. About 60 percent of those are immediate relatives — spouses, minor children, parents — of American citizens, and an additional 30 percent are other relatives, like siblings. The large number of family migrants is an unintended, even ironic, consequence of actions taken by Congress and successive administrations to make life miserable for immigrants regardless of legal status. Legislation enacted in 1996 limited access to federal benefits, curtailed civil rights and increased the risk of deportation. The well-being of foreign nationals was further undermined by the USA Patriot Act in 2001 and was threatened in 2006 by the Sensenbrenner bill, which aimed to deter illegal immigration through strict enforcement of draconian new restrictions; it failed to become law, but a similar strategy underlies Arizona’s 2010 anti-illegal-immigration law. In response, many Mexican permanent residents made an unexpected choice: Rather than leave the United States because they felt unwelcome, they became citizens — a practice known as “defensive naturalization.” In the decade before 1996, an average of 29,000 Mexicans were naturalized each year; since 1996, the average has been 125,000 per year, yielding two million new citizens who could then bring in close relatives. At present, nearly two-thirds of legal permanent residents from Mexico enter as relatives of United States citizens. Another paradox is that many of these new “permanent residents” do not use the visas to settle in the United States; instead, they circulate back and forth as temporary workers — restoring a pattern that had prevailed until the early 1990s, when the United States began trying to seal the border. When returning periodically to Mexico became too expensive, and running the gantlet to get back into the United States too risky, undocumented migrants and their families simply stayed in the United States. But now circularity has returned, and with it a need to reconsider immigration reform. All the major proposals — from Mexico, Congress and President George W. Bush — have included four basic components: reducing illegal immigration; increasing temporary work visas; granting more permanent resident visas; and legalizing existing undocumented migrants. With net migration of undocumented Mexicans near zero and temporary legal migration at record levels, the first two goals have effectively been reached, and mass legal immigration by relatives of citizens satisfies the third. Regularizing the status of the 11.5 million undocumented people who live in the United States has yet to be accomplished, but a solution can be envisioned by recognizing that self-deportation is not going to happen. Voluntary departures have practically stopped, and the idea of forced removals disturbs many Americans. So if legalization can be achieved without too much fuss, the United States and Mexico will have solved their immigration issue peacefully and quietly. It’s a solution long in the making, traceable in part to accident and in part to the hypocrisy of an American policy that has quietly legalized temporary workers without saying so publicly. But timeliness and honesty in these matters are often overrated. However we got here, Mexicans and Americans seem to have an opportunity to put their immigration squabble behind them and live more cordially as neighbors. Jorge G. Castañeda, the foreign minister of Mexico from 2000 to 2003, is a professor of politics and Latin American and Caribbean Studies at New York University. Douglas S. Massey is a professor of sociology and public affairs at Princeton.