The White House has said the decision to challenge Arizona's immigration law was out of its hands, left completely up to Attorney General Eric Holder and the lawyers at the Justice Department. But the implications of the suit filed Tuesday are potentially huge for President Obama and the Democratic Party as the election season begins in earnest later this summer. The federal lawsuit all but ensures a politically charged immigration debate will be in the spotlight in many crucial House and Senate contests. Obama will be called upon frequently in the next several months to make the government's case that the Arizona measure unlawfully preempts federal law. As he campaigns for Democrats at town hall meetings around the country, it will be Obama _ not Holder _ who will be at the center of the intense discussion. A senior Democratic strategist said Obama will probably seek to avoid directly defending the government's suit, or attacking the Arizona law, which remains popular in most polls. Americans largely see the law as an effort to do something about illegal immigration in the wake of federal inaction. Instead, Obama will try to argue broadly about the need for comprehensive immigration reform and will say that the Arizona law does not represent the kind of action that he thinks is needed. 'There is probably some short term pain politically given how popular the law is,' said the Democratic strategist, who spoke on the condition of anonymity because the government lawsuit had not been filed at the time. 'But considering the demographic changes the country is undergoing, long term, there is a lot of upside in advocating for Latinos and comprehensive immigration reform.' The immigration issue is complex and regional, playing out differently in different parts of the country. In border states, anti-immigrant sentiment can run high, but it also often countered by the feelings of large numbers of Hispanic voters. It's an issue that can create political wildfires that are not easily controlled. Sen. John McCain, R-Ariz., found that out the hard way as he started his campaign for president in 2007 by making much the same argument on behalf of comprehensive immigration reform that Obama now advocates. At one town hall meeting after another, anti-immigration activists bombarded McCain with angry comments, even in places _ such as Iowa and New Hampshire _ where his handlers had not expected huge concern about the issue. McCain abandoned his support of an immigration overhaul in the face of the red- hot anger within his party. Since then, the anger has spread more broadly, helping to spark the tea party movement and push immigration to the forefront in several state election races. Now facing a tough primary challenge in his reelection bid, McCain has endorsed his state's law and wants to send thousands of National Guard soldiers to the border. Obama and the White House have sought to position the president as an advocate for greater border security by announcing an increase in the number of national guard troop a at the border. At the same time, Obama is increasingly calling on Republicans to rejoin the fight for an immigration overhaul that McCain and former president George W. Bush once called a top priority. As he did last week, Obama intends to repeatedly remind voters that Republicans such as McCain, who changed their minds, are standing in the way of a comprehensive overhaul of federal immigration policy. The president 'has made clear that his administration will not just kick the can down the road,' White House spokesman Nick Shapiro said. 'Immigration reform is no exception. The president believes that the system is broken and that reform has been held hostage to political posturing and special-interest wrangling.' For some nervous Democratic lawmakers, the focus on immigration could present difficulties getting reelected this November. But party leaders are hoping that the president's rhetoric _ and the decision to challenge the Arizona law _ will help to highlight a serious political challenge for Republicans over the long term. The growth of the Hispanic population, and its support of Democrats in 2008, suggests that Republicans could find themselves in a difficult position if that community concludes that the GOP is not friendly to its interests. 