Evidence keeps accumulating that the tide of immigration is ebbing. Tough enforcement laws passed by states like Arizona and Oklahoma and localities like Prince William County, Va., have reportedly spurred Latino immigrants to move elsewhere. Tougher enforcement of federal immigration laws may be having the same effect.

Classrooms in Orange County, Calif., are suddenly half-empty. Latino day laborers seem to be less thick on the ground at their morning gathering places. Remittances to Mexico and other Latin countries are down, and men are returning to some villages from the United States.

Latinos appear to account for a disproportionate share of mortgage foreclosures. The Census Bureau estimates that net immigration in 2007-08 was 14 percent lower than the average for 2000-07, and those estimates don't cover the period after June 30, when the recession really started hitting.

Demographic forecasters tend to assume that the long-term future will look a lot like the short-term past. That's why the Census Bureau estimates that there will be more than 100 million people classifying themselves as Hispanics in 2050, compared to 45 million today. But history tells us that trend lines don't go on forever. Sometimes they turn around and go downward.

We have had major Latino immigration now throughout the 25 years since the economic recovery of the early 1980s. But I think there is a possibility -- not a certainty, probably not a likelihood, but a serious possibility -- that we may be at an inflection point, at the beginning of a period in which Latino immigration will be substantially lower than it has been the past quarter-century.

We have seen such inflection points in migration before. When Leonard Bernstein wrote "West Side Story" in the 1950s, it seemed that the flow of Puerto Ricans to New York City would continue indefinitely. But in fact net migration from Puerto Rico dropped to just about zero in 1961, when average incomes on the island were about one-third the level of the mainland United States. The huge flow of blacks from the South to the North, which started in 1940 due to the labor demands of war industry and the invention of the mechanical cotton-picker, seemed likely in 1960 to continue on and on. But it stopped suddenly in 1965, the year the Voting Rights Act passed, and today there is a small net migration of blacks from North to South.

Economics plays some role in this. The apparent downturn in immigration in the past 18 months is surely not unrelated to the recession that began, the National Bureau of Economic Research now tells us, in December 2007. The gaming industry in Las Vegas -- then and for most of the preceding 20 years the nation's fastest-growing metro area -- started declining in 2007, and net immigration to Nevada was down 16 percent in 2007-08 from the 2000-07 levels. And reports are coming in of Latinos leaving town as construction of giant hotels on the Strip is shut down by foreclosure.

But immigration is not just about economics. People move, I have come to think, in pursuit of dreams -- or to escape nightmares. One of those dreams -- home ownership in America -- now seems much less attainable than it did just six months ago, with thousands of foreclosures and with subprime loans to low-income buyers presumably a thing of the past. Meanwhile, birth rates in Mexico and much of Latin America took a sharp turn downward around 1990, which means that those entering the workforce there in years hence will have less competition for jobs -- fewer nightmares.

George W. Bush has said that one of his regrets is that he was not successful in getting Congress to pass a comprehensive immigration law, with legalization, guest-worker and enforcement provisions. If Barack Obama and congressional Democrats seek such legislation, they should keep in mind the possibility that the situation they are addressing may be changing. So should those who oppose such a law.

Since Congress considered and failed to pass a comprehensive law in 2006 and 2007, we have learned that tougher enforcement of existing law is possible and can reduce illegal immigration. Now we face a sharply different economic situation, which is presumably less conducive to immigration. This may make the need for a comprehensive law less pressing and at the same time make it politically more palatable.

Our history is one of great surges of migration, immigrant and internal, which begin without much in the way of warning and which end unexpectedly. It's possible -- not certain, maybe not likely, but possible -- that we're witnessing the beginning of one of those endpoints now.