to the cnn research opinion poll in may 50% of those surveyed favored the law and 37% of it opposed it. supporters say that the federal government has failed to enforce immigration laws leaving it to states to pick up the costs of the illegal immigration, and rather than supplanting the immigration policy, arizona's law is meant to supplement it. >> the administration is making both a political, tactical and legal mistake. the arizona law is carefully crafted to work within the context of u.s. immigration law. it is not preempted by federal immigration law. it works in harmony with it. >> reporter: the justice department's lawsuit seeks to have the law thrown out even before it has had a chance to take effect. it is a high bar says the constitutional law professor stephen vladic, but he says it is a strong case. >> well, they are different from first amendment cases as long as the federal government can show that the state law is inconsistent with and indeed in conflict with federal policy,