President Bush came into office promising to fix the country's broken immigration laws that, he said, were preventing willing American employers from hiring willing foreign workers. Nothing could be further from this vision than the employer crackdown that his Department of Homeland Security recently announced.

Why has the administration so totally reversed course?

It is not like it does not understand that the "problem" of illegal immigration is purely a function of existing immigration laws, not "evil doers." These laws don't exactly roll out the welcome mat for high-skilled immigrants that California's Silicon Valley badly needs. But they are downright hostile toward "unskilled" workers who form the backbone of the agricultural, landscaping and hotel industry in the Golden State and elsewhere.

On paper, there are two types of visas available for unskilled workers: H-2A for campesinos, or farm workers, and H-2B for other seasonal jobs. But thanks to copious red tape, these visas rarely ever arrive on time for the job. Even worse, they are usually good for less than a year and can only be renewed a few times. Once they expire, workers have to return home because neither they, nor their employers, can apply for a green card or permanent residency. Such a dead-end process leaves workers no choice but to work illegally.

The White House tried to get Congress to pass comprehensive immigration reform with a guest worker component to create a way for future foreign workers to legally live and work in this country – and also regularize the status of undocumented aliens already in the country. But GOP nativists – aided by conservative talk radio and some Democrats – killed the bill as "amnesty," insisting instead on a tough, enforcement-only approach.

The Homeland Security Department's employer crackdown effectively embraces their approach. In 30 days, the Social Security Administration (SSA) will start sending letters to employers alerting them to any discrepancy in the Social Security numbers their employees are using and government records. Employers who discover that employees have given them false numbers – something that undocumented workers often do -- will be required to fire them within 90 days – or face up to $10,000 in fines per employee. Repeat violations could bring jail time.

Michael Chertoff, the Secretary of Homeland Security and the architect of the crackdown, noted that the SSA expects to send 140,000 of these "no-match" letters covering more than 8 million people. But how precisely any of this will enhance national security, the core reason why his department exists, he has yet to explain. Does he really believe that Al Qaeda operatives are holding jobs illegally and will drop their plans to scurry for the border once these letters start rolling in?

This crusade won't improve national security, but it will disrupt the economy. To the extent that it succeeds in slowing the tide of foreign immigrants, it will cause labor shortages and raise prices of produce -- and other goods and services in immigrant-dependent industries. California employers, especially farmers, will be among the worst hit given that they employ 2.5 million illegal immigrants – the highest of any state. Even before the crackdown, California's farmers were projecting 30 percent crop losses because intensified border patrolling had already shrunk the labor pool this year. Dianne Feinstein, California's Democratic Senator, expects the situation now to be nothing short of "catastrophic."

Curiously, Commerce Secretary Carlos Gutierrez, who joined Chertoff in announcing the crackdown, doesn't deny any of this. "We do not have the workers our economy needs to keep growing," he readily admits.

So why drive out the workers we have? Employer sanctions have been on the books for years. Why enforce them if there are no upsides for national security – only downsides for the economy?

One explanation is that the administration is hoping that this campaign will prove to Congress how much the economy depends on undocumented workers and force it to once again tackle comprehensive immigration reform. However, it is highly doubtful that the administration can genuinely believe that driving California farmers out of business will convince a determined immigration foe like Republican Rep. Tom Tancredo of Colorado to see the light.

The only plausible reason is that the administration has not just abandoned rational immigration reform, which would be understandable under the circumstances. It has actually made a conscious decision to embrace its opposite to win back its lost base before next year's elections. In short, its immigration policy now is driven neither by conviction, nor the needs of the economy - but naked political calculation, even if that involves targeting "willing employers" and "willing foreign workers," the very victims of that policy.

That is a new low.