White House staffers are hard at work deliberating about what should go into the executive order the president is expected to issue after Labor Day: his do-it-yourself, go-it-alone version of immigration reform. The smart money is betting the president will grant some sort of temporary legal status to as many as 4 million unauthorized immigrants.

This would be a huge relief for those who qualify and their families. There won’t be a path to citizenship — only Congress can provide that. But together with the president’s 2012 memo granting legal status to young people brought to the U.S. illegally as children, it could allow more than a third of the nation’s unauthorized immigrants to remain in the country and work legally without fear of being deported.

Immigrant rights advocates will be thrilled. Though they’d like the number to be bigger, this is the fix they’ve been fighting for, in some cases for more than a decade. But is it really a solution? The answer, sadly, is no.

An executive order mandating legalization alone won’t address what’s wrong with the immigration system. And the danger is that once Obama acts, that may be the end of what Washington does to address the issue — this year or for many years to come.

A one-time legalization would ameliorate a symptom of what’s broken. But it would do nothing to tackle the underlying cause: the dynamic that draws immigrants to come to the U.S. illegally in the first place — supply and demand. Most people come to work, drawn by our need to fill jobs for which there are no willing and able Americans.

Some of these jobs require highly skilled employees — PhD scientists or IT technicians. But the overwhelming majority are for low-skilled workers: physically demanding, often outdoor work that holds little appeal, at any economically plausible wage, for increasingly educated American workers.

The problem is that under current law there is virtually no legal way for less-skilled foreigners to enter the country to work in year-round jobs. And because they can’t get in the front door, they come through the back door — illegally.

Obama is not the first policymaker to have trouble grasping this reality. Washington made exactly the same mistake once before — with the 1986 Immigration Reform and Control Act.

In the 1980s, as over the past decade, many reformers argued that any overhaul should include three core components: tougher enforcement of immigration law, some kind of legalization or regularization for immigrants living in the country illegally and changes to the legal immigration system — including more worker visas — to prevent future illegal immigration.

Immigrant rights advocates called for regularization — in those days, it was officially called “amnesty” — and they had the political power to back their demands. Then as today, immigration hawks drove a hard bargain: no amnesty without beefed-up enforcement, and they too had the muscle to get most of what they wanted.

But in the 1980s, as today, the third component was the least compelling politically. Those arguing for fixing the system lacked the juice to get what they wanted into the bill, and the 1986 act did little to accommodate new legal employment-based immigration.

We all know the consequences. A generation later, America is once again home to a vast underground population of unauthorized workers.

Fast forward to today’s debate. It’s deja vu all over again. Immigrant rights advocates want regularization and have the political power to force Obama to come through with it. Immigration hawks want more enforcement, and you can be sure they’ll have the power to convince Congress to come through with that in the wake of the president’s executive order.

But once again the argument for fixing the system is all but sure to fall through the cracks. Though the president may throw in some additional visas for highly skilled immigrants, his allies in the union movement will be sure to block more visas for less-skilled workers.

Bottom line, once again, we’ll deal with one symptom of the broken system — the 11 million who entered illegally in past decades because there was no legal way to get here. But we’ll do nothing to solve the underlying problem.

The silver lining, if you want to call it that: We’re sure to get another crack at the underlying problem when the issue arises again, unavoidably, in a decade or two. That’s when the country will once again confront the consequences of failing to create a workable legal system - after another 11 or 12 or who knows how many million new unauthorized immigrants have come to the work in the U.S. illegally.

Tamar Jacoby is president of ImmigrationWorks USA, a national federation of small-business owners in favor of immigration reform. Jacoby wrote this for the Los Angeles Times.