NOBODY KNOWS for sure how much weight, or blame, to assign each of the factors that have contributed to the flood of unaccompanied children and teens crossing the U.S.-Mexico border in recent months. The surge of illegal entries has crested into a full-blown immigration crisis, the resolution of which now depends on the unpromising hope of cooperation between the Obama administration and Congress.

Since the fall, some 52,000 undocumented youngsters, most from Central America, have poured across the border — about five times more than crossed in all of fiscal year 2012.

President Obama is right to have declared that unacceptable and to insist on restoring order along the border. But the solution he has proposed, reasonable as far as it goes, is incomplete.

Many of the youthful border crossers are driven to undertake the perilous journey by the “push” of lawlessness, drug violence and sex trafficking in Central America. And many appear to be encouraged to risk the trip by the “pull” of overburdened U.S. immigration courts and the unforeseen consequences of U.S. laws and lax patterns of enforcement that have allowed tens of thousands of young immigrants to stay in this country after entering without documentation. Democrats and Republicans share responsibility for those laws.

Some of those seeking a foothold in this country also may mistakenly believe that they will be covered by Mr. Obama’s 2012 order granting a reprieve from deportation to children and teens who arrived before 2007.

Brayan Duvan Soler Redondo, a 14-year-old Honduran boy, overlooking the Rio Grande. (Joshua Partlow/The Washington Post)

A more likely culprit is legislation approved by Congress with bipartisan support in 2008, which was intended to protect minors from sex trafficking and other abuses. That law, signed by President George W. Bush, allows undocumented immigrants from non-border states — including the Salvadorans, Hondurans and Guatemalans who constitute most of the current wave — to have their cases heard by an immigration judge . As the backlog of cases mounts, the minors are admitted into this country while they await a hearing, which may take months or years.

Last week, Mr. Obama wrote to Congress saying he would seek to modify that law. Yet he made no such request Tuesday when he instead proposed some $3.7 billion in spending to add immigration judges and other personnel and to house, feed and care for the minors who have already crossed the border.

That seems unlikely to send the get-tough message Mr. Obama promised. The fact is that since he entered office, shortly after the 2008 law took effect, the number of undocumented youths deported or turned back at border posts has plummeted, according to government figures released to the Los Angeles Times.

Mr. Obama has come under intense pressure from Democrats and immigration advocates to continue this leniency. They make their argument on humanitarian grounds. But there is nothing humanitarian in tacitly encouraging tens of thousands of children to risk their lives, often at the hands of cutthroat smugglers, to enter this country illegally.

If the president is serious about restoring order to the border and dissuading children and their families from a costly and life-threatening trip, he will add teeth to his policy by seeking the legal change he promised.