Politics is about seizing opportunities.

When a California health insurance company hiked individual premiums as much as 39 percent in February, congressional Democrats seized the opportunity to showcase the urgency of health care reform. Last month, when the Securities and Exchange Commission filed suit against Goldman Sachs alleging fraud, Democrats seized the opportunity to build momentum for financial regulation.

Now Democrats are warning that the federal government had better pass reasonable legislation to deal with illegal immigration, or else. Or else what? Or else more states could pass Arizona-style immigration laws that threaten to turn America into a police state. The Arizona statute authorizes the police to detain anyone who appears to be an illegal immigrant and isn't carrying documents that prove otherwise.

President Obama seized the issue immediately, just as Republican Gov. Jan Brewer was signing it into law. "Our failure to act responsibly at the federal level will only open the door to irresponsibility by others," the president warned. "We will continue to see misguided efforts ... around the country." Likewise, House Speaker Nancy Pelosi, D-Calif., called the Arizona law "misguided and irresponsible." Tim Kaine, chairman of the Democratic National Committee, also condemned it as "misguided."

The federal courts are likely to strike down the Arizona statute as unconstitutional. The law is also likely to carry a high cost for Arizona. Latino leaders are already calling for an economic boycott of the state. Mexican tourism might dry up. The Mexican Senate had voted unanimously to urge Brewer to veto the bill, and Mexico's foreign affairs ministry warned that the law could damage U.S.-Mexican relations "for generations."

Then there's the cost of enforcing the law -- as well as defending its constitutionality and fighting lawsuits filed by U.S. citizens who say they have been victims of racial profiling. Add to all that the satire and ridicule that the national media is already heaping on the state.

Will the law even work? Not likely. Every previous crackdown on illegal immigration has produced unintended consequences. The federal government's Operation Gatekeeper in the 1990s shut down points of entry in California, New Mexico, and Texas. The result was to shift the illegal immigration problem to Arizona's Sonoran Desert, the most isolated and hazardous area along the U.S.-Mexico border.

Tougher border controls have made it difficult for illegal immigrants to return to Mexico. Traditionally, migrants have gone back and forth, depending on the availability of jobs. Now, once they're here, they stay.

The issue reached a boiling point this year after rising drug violence in Mexico heightened fears in U.S. border areas. Arizona's conservatives demanded action and got it. The Republican-controlled Legislature has passed similar laws before, but Democratic Gov. Janet Napolitano vetoed them because, in her view, "they would have diverted critical law enforcement resources from the most serious threats to public safety." Brewer, her Republican successor, faces a primary challenge from the right. So does Republican Sen. John McCain, who once co-sponsored comprehensive immigration reform that would have provided a new path to citizenship; these days, he supports the state's new law.

The response from Republicans around the country has been muted. Not so from Democrats, particularly those in areas with a large or growing Latino vote. That group includes Senate Majority Leader Harry Reid, who is facing a tough re-election battle in Nevada this year. Reid is insisting on putting immigration reform ahead of climate-change legislation in his chamber. He has pledged to bring an immigration bill to the Senate floor after Memorial Day, whether or not it has bipartisan support.

There probably won't be. Sen. Lindsey Graham, R-S.C., who was part of a trio working on a bipartisan climate bill, denounced the Democrats' focus on immigration reform as "a cynical political ploy." In the short term, Republican incumbents have to worry about angering their right flank in the primaries. In the long run, the GOP has to worry about alienating Latinos, the nation's largest and fastest-growing minority.

In 1994, 59 percent of Californians voted for Proposition 187, which denied public services to illegal immigrants. The measure helped Republican Gov. Pete Wilson get re-elected that year. But courts eventually struck Prop 187 down. The long-term effect was to rally millions of Latino citizens to register and vote -- and to turn Ronald Reagan's home state into a Democratic stronghold. As California went, so could go Arizona, not to mention Colorado, Florida, and Nevada.

This article appeared in the Saturday, May 1, 2010 edition of National Journal.

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