The Senate takes up "comprehensive" immigration reform again this week. But the meat's still missing in this burrito. As Mexico's ambassador to Washington warns, even the "rosiest, peachiest" reform in the US won't end the flow of poor migrants. Reform must also take place in Mexico.

And begun it has.

For the past seven months, Mexico has been at war with itself, literally. A new president, Felipe Calderón, has dispatched 24,000 troops into battle with the most corrosive influence in Mexico's economy: powerful drug cartels.

These violent syndicates, which mainly transport drugs into the US, have exploded in the past decade. They've escalated crime and political corruption, hindering creation of well-paying jobs for would-be migrants. At election time, they provide cash for many campaigns.

This domestic war, which resembles the Iraq war in tactics and killing rates, was Mr. Calderón's opening gambit for wholesale reform. It is widely popular but faces an uncertain future. The cartels are fighting back with gruesome murders. And the Army, one of the few respected institutions in Mexico, is not good at policing, a task it must do to root out local drug networks. Some of its elite soldiers have joined the cartels.

Still, the war gives Calderón enough public support to conduct a quiet and pragmatic battle with the ruling opposition in the legislature. In March, he was able to win reform of state pensions. This week, he will propose tax hikes to reduce the government's risky reliance on oil-export revenues. And he was helped this month by a Supreme Court ruling that struck a blow at the broadcasting giant Televisa, one of many monopolies controlled by powerful, vested interests.

Opening up these key parts of the economy – telecommunications, oil, cement, and electricity – to fair competition under the law would be Calderón's greatest legacy. It would build on two other major reforms: the opening of Mexico's markets since the mid-1990s through NAFTA and the establishment of real democracy with the end of one-party rule in 2000.

Any reforms would do little to stem migration, however, unless they reach the poorest regions in the south, such as Chiapas and Michoacán. These areas are the main source of migrants to the US, and a better economy there would help keep valuable workers in Mexico. Among his reforms, Calderón has offered help to young entrepreneurs and launched job-training programs.

How can the US help? For one, effective border enforcement would keep more Mexicans in Mexico where they can contribute to the economy. The US can also better crack down on the flow of arms to Mexico's cartels and the flow of drugs into the US.

Mexico doesn't require a mini-Marshall plan from the US, as some suggest – the kind that Colombia has received to fight off its drug cartels. That $5 billion project entailed the use of American troops to help the war against Colombian rebels. Mexico hardly needs GIs on its soil. And as one of the world's 15 largest economies and an oil exporter, it doesn't need money – just reform.

The US Congress should see its immigration reform in the larger picture of Mexico's needs. The ultimate solution truly lies south of the border.