Demonstrators picket against the possible arrivals of undocumented migrants who may be processed at the Murrieta Border Patrol Station in Murrieta, California July 1, 2014. Some 140 undocumented immigrants, many of them women with children, will be flown from Texas to California and processed through a San Diego-area U.S. Border Patrol station as federal officials deal with a crush of Central American migrants at the border, a local mayor said on Monday. (Sam Hodgson/Reuters)

STYMIED BY congressional paralysis, President Obama is reportedly considering unilateral action to address — though surely not fix — the nation’s immigration policy mess and the more recent surge of minors streaming across the southwestern border.

The president’s frustration is understandable. Faced with a genuine humanitarian crisis, Congress’s failure to pass a workable fix is unconscionable. In the Republican-controlled House, the GOP bowed to its most extreme lawmakers in passing measures that have zero chance of becoming law — and would have paved the way for deportations of blameless young people raised in this country after being brought here by their undocumented parents. In the Senate, the intransigence of both parties yielded no bill at all.

Obstinate, hopelessly partisan and incapable of problem-solving, Congress is a mess. But that doesn’t grant the president license to tear up the Constitution. As Mr. Obama himself said last fall: “If, in fact, I could solve all these problems without passing laws in Congress, then I would do so. But we’re also a nation of laws.” To act on his own, the president said, would violate those laws.

Mr. Obama now seems to be jettisoning that stance in the name of rallying his political base. He is considering extending temporary protection from deportation to millions of illegal immigrants, including the parents of U.S.-born children and others who have lived in the United States for years. Conceivably, this would give Democrats a political boost in 2016. Just as conceivably, it would trigger a constitutional showdown with congressional Republicans, who could make a cogent argument that Mr. Obama had overstepped his authority.

The president should think twice. Some of the same Democrats and pro-immigrant advocates urging him to protect millions of undocumented immigrants from deportation would be outraged if a Republican president took a similarly selective approach to enforcing the laws — say, those that guarantee voting rights or prohibit employment discrimination. Mr. Obama’s instincts — “we’re also a nation of laws” — were and remain correct.

Even without congressional action, the president can do certain things to ease the immigration crisis. He can ensure that the tens of thousands of unaccompanied Central American children who have streamed into the country are treated humanely and accorded due process in the immigration courts under existing law.

He can push ahead with a plan under review to screen such children in Honduras — where many come from — so they don’t risk their lives crossing Mexico to reach the United States.

And as long as Congress fails to provide sufficient funds to cope with the flood of underage kids, the president can transfer enforcement resources to the border from the interior.

Mr. Obama’s own vacillations have not helped cope with the crisis. He was right to identify a 2008 anti-trafficking law as a key source of the problem. Inadvertently, that law has encouraged thousands of Central American children to try to reach the United States by granting them access to immigration courts that Mexican kids don’t enjoy; the effect has been months-long backups in the courts. Initially, the president said he would propose changes to the law to hasten deportations. Faced with opposition from Democrats, he backed down days later.

The right response to the collapse of the U.S. immigration system is for Congress to fix the law. The House had a vehicle to do just that by taking up the legislation passed by the Senate last year. But it does not follow that Congress can be ignored based on its failure to act. The right response to lawmakers who won’t solve the immigration mess is to replace them with ones who will.