Now that Arizona's immigration law has at least temporarily been put on hold, President Obama may well be tempted to put the whole immigration issue on the back burner for a while, as his Justice Department's lawsuit against the state winds its way through the courts. After all, he has plenty of other things vying for his attention – two wars and an anemic economy, for starters. 

Who could blame him for wanting to put aside the contentious issue of immigration?

But doing so would be a mistake.

Both politically and as a policy matter, the president needs to remain engaged on immigration. The lawsuit has simply reinforced in the public mind the impression that this administration isn't serious about enforcing immigration laws. And such a lack of credibility is precisely the obstacle to the president's own goal of amnesty – my own skepticism about amnesty notwithstanding, much of the public would grudgingly accept it if they believed the government was now firmly committed to enforcing immigration laws in the future.

The White House understands the need to address this credibility gap on enforcement, but the president's appointees can't help themselves – they recoil from the very idea of enforcement. And if they can't get Congress to amnesty all the illegal aliens (and thus eliminate the need to enforce the law), then they want to try to do it through the back door without congressional approval, as an internal administration memo recently obtained by Sen. Charles Grassley spelled out. Thus only by remaining engaged, and constantly pushing his unwilling subordinates to enforce the law, does he have any chance of eventually reaching his goal of legalizing at least some portion of the illegal population.

But more importantly, the immigration issue can't be left in limbo because its policy consequences are huge. We have some 11 million illegal aliens in the United States who, because of their low levels of education, represent a significant burden on taxpayers. The majority of families headed by illegal aliens live in or near poverty and are uninsured, which is why fully 40 percent of them use at least one major welfare program. And it's their presence here, not mainly their legal status, which creates these costs; for instance, if they were to be legalized, an estimated 3.1 million would qualify for Medicaid, costing more than $8 billion each year.

What's more, the 7 million or so illegal aliens who have jobs are competing directly with less-educated and young American workers, whose unemployment rate is twice the national average. 

For teenage workers, less-skilled immigration (much, though not all, of it illegal) has caused a significant decline in the percentage of American teenagers able to find summer jobs. And there's no surprise here – in the top ten summer occupations for U.S. teenagers, immigrants make up one out of five workers, fully developed adults competing with kids for work.

And don't forget the security threat posed by illegal immigration. Any system that a Mexican busboy can sneak through is one that an al Qaeda terrorist can also sneak through. Just last month, a Hezbollah official was arrested in Mexico seeking to use Lebanese immigrants communities there as a base to set up operations in Latin America. Mahmoud Kourani, a “member, fighter, recruiter and fund-raiser for Hezbollah” according to his federal indictment, was smuggled across the Mexican border. And these are a few of the ones we know about; what about those we don't know about – yet? In an age of terrorism combined with cheap transportation and communications, immigration security is national security.

Leon Trotsky once said that you may not be interested in war, but war is interested in you. By the same token, President Obama may not be interested in immigration, but it's interested in him, and the only sensible course is to be proactive and aggressive in enforcing immigration laws, both for the good of the country and for his own political self-preservation.

Mark Krikorian is executive director of the Center for Immigration Studies.

Fox Forum is on Twitter. Follow us @fxnopinion.