When Arizona Gov. Jan Brewer signed Arizona’s controversial new immigration law last week, she didn’t only launch a new era of police profiling in the Grand Canyon State. Brewer also may have fired the first shot in the political battle over immigration in the 2010 elections.

Suddenly, the White House sprung to action, with President Obama chiding Arizona for the law and the administration signaling it would push for immigration reform legislation out of Congress this summer. “Our failure to act responsibly at the federal level will only open the door to irresponsibility by others,” he said Friday. “And that includes, for example, the recent efforts in Arizona, which threatened to undermine basic notions of fairness that we cherish as Americans, as well as the trust between police and their communities that is so crucial to keeping us safe.” As a candidate, Obama had promised to work on immigration during his first year in office; healthcare devoured most of 2009, but now the administration seems ready to move.

The Arizona law could galvanize Latino voters even more than a revived effort to pass comprehensive immigration legislation (which collapsed in the Senate twice in 2006 and 2007). “The rhetoric that the Republicans have made of the immigration issue — which is not only anti-immigrant but seen and perceived as anti-Hispanic — impacts all Hispanics,” says Fernand Amandi, a Democratic pollster with Bendixen Amandi, a Miami-based firm that focuses on Latino voters and has been part of briefings on the issue at the White House. “It’s an absurd political calculus.” Some Republicans seem aware of the dangers, as well; former Florida Gov. Jeb Bush told Politico Tuesday the Arizona law wasn’t “the proper approach,” and Florida conservative wunderkind Marco Rubio, whose family is Cuban, also came out against it.

But other Republicans have been vocal in supporting it. “It has a 70 percent approval in Arizona and I think that we ought to respect the people of Arizona in their right to make their own decisions,” House Minority Leader John Boehner, R-Ohio, told reporters. One GOP candidate for Alabama’s governorship, Tim James, has a TV ad up demagoguing the issue and promising only to give driver’s license tests in English if he wins: “This is Alabama. We speak English. If you want to live here, learn it.” (The fact that Census data shows less than 4 percent of Alabama residents don’t speak English at home, well below the national average of 17.9 percent, is probably the biggest tip-off that the ad is more about pushing conservative hot buttons than solving pressing local issues.)

In the long run, immigration could be a winning issue for Democrats — Hispanics are the largest, and fastest-growing, minority group in the country, and the more the GOP pushes draconian border control measures, the less likely they are to win Latino votes. In some states this fall, immigration could help bring some 2008 voters back into an otherwise low-turnout election. But in other places, tough talk might help Republicans get their own base to the polls. With all that in mind, here’s Salon’s guide to five spots where immigration could be an issue in the November elections. (We’ve listed what the Hispanic share of the electorate could be in 2010, as calculated by Bendixen Amandi, using demographic data and voter registration statistics.)

Arizona: The state has been the center of the immigration debate for a while, but now the issue could drive both a Senate race and a governor’s campaign. Former Rep. J.D. Hayworth, who’s no stranger to immigrant-bashing for political gain, has been hounding Sen. John McCain mercilessly on border issues in the Republican primary. McCain, in turn, has been lurching further and further away from the reform legislation he wrote four years ago; he called last week for Obama to send National Guard troops and 3,000 new Border Patrol agents to the U.S.-Mexico frontier. On the Democratic side, the Arizona law drew another potential candidate, immigration activist Randy Parraz, into the race on Tuesday. If McCain wins the GOP primary, chances are he’ll win in November easily, but if Hayworth somehow pulls off his right-wing challenge, the race could become a target for Democrats — and Arizona’s Hispanic voters.

Meanwhile, Brewer, a Republican, appears to have dramatically improved her standing with white voters since the fall — in part by signing the bill. She still trails Democratic nominee Terry Goddard in some polls, but one recent survey found her ahead, and far more popular than she had been before the law passed. Expect both sides to talk about immigration constantly in the fall. Hispanic share of electorate: 15 percent.

Nevada: There’s a good political reason for Senate Majority Leader Harry Reid to push for an  immigration reform bill, policy questions aside: In the 2008 presidential election, exit polls showed 15 percent of Nevada voters were Latino — and 67 percent of Latino voters backed Obama. Reid, whose bid for reelection is in trouble, would love to pick up an issue that can help bring some of those voters back to the ballot boxes in November. That prospect, in fact, appears to have unsettled Reid’s Republican challengers, who came out firing last week against an immigration reform bill. “His thinking is that if he offers amnesty, somehow that will ingratiate him with the populace here in Nevada,” said GOP candidate Sharron Angle. Hispanic share of electorate: 12 percent.

California: About 15 years ago, California was a classic purple state: Republicans and Democrats competed seriously for the state’s presidential votes, Senate seats and statehouse. And then the California GOP establishment backed Proposition 187, designed to keep undocumented immigrants from using social services in the state, and sparked a furious backlash from Latino voters. Since then, the only Republican to win a statewide race at the top of the ticket was Gov. Arnold Schwarzenegger — himself an immigrant.

Which means Democratic Sen. Barbara Boxer, who’s never been in weaker shape heading into an election, may join Reid in trumpeting her work on behalf of immigration reform if a bill does come back to the floor this year. Immigration could be an issue in the governor’s race, as well; the Republican field has been dashing to the right to win the nomination to take on Attorney General Jerry Brown, which may not endear them to Latino voters come the fall. Hispanic share of electorate: 18 percent.

Florida: It won’t be as easy for Democrats to motivate Latinos by highlighting GOP opposition to immigration reform here if Rubio is the Republican Senate nominee. Rubio, in fact, offers the best hope for Republicans to undo the damage that initiatives like the Arizona law have done to the way they’re seen by Latinos — like Mel Martinez, who retired last year, he would be the only Hispanic Republican in the Senate (and one of only five in Congress).

Votes from Latinos and other immigrants helped Obama win Florida in 2008; campaign rallies in Miami featured signs written in Haitian Creole. If the issue does become a battleground, the Senate and governor’s race here could get drawn in. Hispanic share of electorate: 13 percent.

Indiana: Republicans aren’t the only ones divided by immigration. In Indiana, Democratic Senate nominee Brad Ellsworth, a former sheriff, won his House seat a few years ago in part with rhetoric on border security that would have sounded at home in a Tom Tancredo campaign ad. Here, and in states like Ohio, Arkansas and Kentucky where Democrats are also hoping to win Senate races, their candidates are likely to run as far away from comprehensive immigration bills as the Republicans do. In places where Obama and the national Democratic Party aren’t particularly popular, having Democratic leaders in Washington push an immigration reform bill probably helps Republicans. Hispanic share of electorate: 4 percent.

Other places to watch: Colorado’s Senate race could be close, and like Nevada and Arizona (and New Mexico, which sent Democrat Tom Udall to the Senate in 2008), the demographics in the state are tilting in favor of Democrats. Bendixen Amandi estimates 10 percent of the electorate will be Hispanic this year. Texas, where Democrats think they have a shot at beating Gov. Rick Perry, will have an electorate that’s 22 percent Hispanic — if the state isn’t quite a battleground yet, it will be if the current demographic and political trends continue.

In House races in states like Ohio and Pennsylvania, Republicans could get some traction from opposing immigration reform. Hazelton, Pa., Mayor Lou Barletta — a hero to border security hard-liners for his attempts to ban landlords in the town from renting to undocumented immigrants — is running against Democratic Rep. Paul Kanjorski again; add immigration to a bad climate for Democrats in general, and he may have a shot. Likewise, some districts in the Southwest could see Republicans pushing for tougher border restrictions. But that won’t help the GOP’s long-term problem with Latino voters.

Arizona’s governor vows the state’s tough new law targeting illegal immigration will be implemented with no tolerance for racial profiling, but at least two advocacy groups were preparing legal challenges and Mexico has warned that the law could affect cross-border relations.

Republican Gov. Jan Brewer on Friday signed into law a bill that supporters said would take handcuffs off police in dealing with illegal immigration in Arizona, the nation’s busiest gateway for human and drug smuggling from Mexico and home to an estimated 460,000 illegal immigrants. The law requires police to question people about their immigration status — including asking for identification — if they suspect someone is in the country illegally. It’s sparked fears among legal immigrants and U.S. citizens that they’ll be hassled by police just because they look Hispanic.

Gov. Jan Brewer ignored criticism from President Barack Obama on Friday and signed into law a bill supporters said would take handcuffs off police in dealing with illegal immigration in Arizona, the nation’s gateway for human and drug smugglers.

With hundreds of people surrounding the state Capitol, protesting that the bill would lead to civil rights abuses, Brewer said she wouldn’t tolerate racial profiling. She said critics were “overreacting.”

“We in Arizona have been more than patient waiting for Washington to act,” Brewer said after signing the law. “But decades of inaction and misguided policy have created a dangerous and unacceptable situation.”