It would be the biggest change to the enforcement of immigration law in 20 years.

To bring lawmakers on board, the president worked the phone. He buttonholed senators.

It was 2007. President George W. Bush’s proposal to grant amnesty to millions unlawfully present in the United States was up for a vote.

It lost. One-third of Senate Democrats voted against the procedural motion to move the bill. Some of the president’s own party balked as well.

Now President Obama has his staff looking for loopholes in the law that would let him give “administrative” amnesty to millions of illegal immigrants. If Congress won’t do it, he argues, then he must.

That makes no sense. If Americans really supported amnesty, lawmakers would have given them what they wanted rather than spend the past seven years arguing about “comprehensive” immigration reform. Even if only liberal lawmakers thought amnesty was a good idea, it would have been a done deal five years ago when Democrats controlled both houses of Congress and the White House.

Obama has already been down the “unilateral amnesty” road before, with his Deferred Action for Childhood Arrivals program. That administrative decree is widely credited with fueling the flood of adolescent immigrants now washing illegally over our southern border.

This unintended consequence (amnesty encourages more illegal entries) has left Americans even more concerned about border security than they were seven years ago. Today, most Americans are demanding the deportation of illegal immigrants. Even legal immigration has become less popular.

Obama’s immigration and border security policies have proved divisive and destructive. Rather than bringing Americans together to look for solutions, he is tearing them apart — appeasing some while demonizing those who oppose him.

Imposing an “administrative” amnesty would ignore both the will of the American people and the role of Congress in lawmaking. If Obama acts in this imperial fashion, he will so poison the well of immigration politics that it could take decades to rebuild a consensus on immigration reform and border security policy.

Politics aside, there is no rational argument for an administrative amnesty. It is not fair. It won’t be cheap. And it won’t work.

The United States already accepts about 1 million legal immigrants a year. That’s more than any other nation. Yet it’s a clunky and at times illogical process, not nearly as efficient as the systems in Canada or Australia. And, there is a backlog of millions waiting to come in. Real reform would seek to make our legal immigration system work better — not ignore it and the millions willing to play by the rules to enter our country.

Nor is the president’s proposal just. A just government applies the law equally to all. Obama’s approach picks winners and losers.

And, it’s expensive. Application fees won’t cover the cost of processing millions of amnestied illegals, much less clear the backlog of some 4.3 million waiting in line for green cards.

Moreover, a presidential amnesty will do nothing to achieve the single immigration reform that commands the broadest support among the American public: a more secure border.

Most Americans want immigration laws that work. And they want them enforced.

Not since Franklin Roosevelt tried to pack the Supreme Court has a president so blatantly ignored the people’s will to impose his vision of what’s best for America. Obama seems insensible to how deeply offensive most Americans find an overreach of presidential power.

In pursuing “administrative amnesty,” Obama risks more than flushing away any chance of Washington working out reasonable immigration and border security reforms. He risks alienating the vast majority of the American public.

JAMES JAY CARAFANO, a Washington Examiner columnist, is vice president for defense and foreign policy studies at the Heritage Foundation.