If the 2008 presidential election was nearly derailed by absurd posturing about “God, guns and gays,” look for this year’s contest to ballyhoo illegal immigration.

The stage was set by the 2010 midterm elections, as several states enacted draconian anti-immigrant measures. The worst was Arizona’s, which tasked police with ascertaining the legal status of people they stop for any reason, and required that they detain anyone with the “reasonable suspicion” of being in the country illegally. It also empowered citizens to sue police if they failed to comply.

The 9th U.S. Circuit Court of Appeals blocked many of the law’s most egregious provisions from being implemented. If it were allowed to stand, the law’s most notable effect would be to make life very unpleasant for anyone unlucky enough to look or sound like an illegal immigrant. But that may have been the point to begin with.

The Arizona law will come under scrutiny at the federal level later this month, both in the Supreme Court and in Congress. On April 25, the Supreme Court will hear arguments on whether Arizona has pre-empted the federal government’s longstanding powers to enforce immigration policy. The U.S. Department of Justice has brought the suit. The day before the court hearing, a Senate subcommittee headed by Democrat Charles Schumer will do some political grandstanding on the issue in a hearing of its own.

Schumer sent a letter to Arizona Gov. Jan Brewer asking her to testify. Specifically, he asked her to comment on whether the law is still necessary, given $600 million in enhancements to border security that he helped pass. Brewer declined.

Schumer’s kidding, right? Of course Brewer’s not going to back down on her state’s law. To do so would give up her law-and-order credentials. Few issues stoke the GOP base as much as tough talk about illegal immigration. The party is counting on the issue to keep people fired up and ready to donate this year.

A point that the Justice Department will make before the Supreme Court is that the Arizona law does nothing to solve the very real problems the state and many others have with illegal immigration.

Arizona can’t deport people. That’s the role of the federal government. Nor can it decide who is granted legal status, or take that status away. It doesn’t control who is given a visa, work authorization or asylum. And it certainly can’t do much to address the problem at the heart of the immigration issue: our country’s need for low-wage labor, and the lack a legal framework for bringing in guest workers.

Arizona, a state heavily dependent on tourism, restaurants and hotels, needs such workers. It can’t get enough of them legally, any more than states like Georgia can, with its reliance on immigrant labor for agriculture. Nothing state legislators conjure and pass into law can change that fact.

From a practical, real world understanding of how immigration enforcement works, the Arizona law is a trainwreck. The American Bar Association, the United States Conference of Mayors, the National League of Cities and more than 40 attorneys general have filed amicus briefs supporting the government’s arguments against the Arizona law. (A separate lawsuit, filed by a coalition of nonprofits, argues that the design of the Arizona law will certainly lead to routine civil rights violations.)

From a political point of view, however, it’s excellent grist for the mill of conservative demagoguery. Republicans in several other states, including Utah, South Carolina, Alabama and Georgia have passed or are contemplating similar measures. They will be closely watching the case.

If the U.S. Supreme Court fails to strike down the Arizona law, it will give state after state carte blanche to pass its own version of this wrongheaded law. The country will wind up with a mishmash of varying policies, mostly based on the fantasy that 12 million people, some with longstanding ties and U.S.-born children, are going to pack up and leave.

Brewer argues that it was failure at the federal level that created the illegal immigration problem. And she’s right.

However, only federal action can fix this problem. And on this point, the U.S. Supreme Court must unequivocally set the states straight.

Then Congress has to get to work. No excuses.