Responding to President Trump's offer of assistance following the massacre on Monday of six children and three women who were all American, President Andrés Manuel López Obrador said he will respond "independently and asserting our sovereignty."

If he really wants to go there, then the United States should independently assert its right to defend its citizens.

There is no question that the American people bear some responsibility for Mexico's terrible drug wars — we are the ones lining cartel pockets by buying the drugs. But this latest attack offers stark proof that U.S. national security faces an intolerable threat. If López Obrador wants to maintain his idiotic and immoral "hugs not bullets" strategy toward the cartels, that is his prerogative as Mexico's democratic leader. But America must defend its citizens.

The images and witness accounts from the attack scene are terrible. The victims' SUVs are burnt out and littered with hundreds of bullet holes. One family member told the New York Times that babies in one of the cars were burned alive as they sat stuck in their seats.

This must not be allowed to stand.

As a first step, President Trump should make clear to López Obrador, known universally in Mexico as AMLO, that he must identify the cartel responsible. Based on the location of the attack, along the state borders, the primary suspects are the Juárez Cartel and the Sinaloa Cartel. Regardless, Trump should push López Obrador to have the federal police work alongside joint investigative teams from the Drug Enforcement Administration, the CIA, and the FBI's Critical Incident Response Group. He should demand that U.S. agencies receive access to all necessary intelligence and support.

And once the culpable cartel is identified, López Obrador should move to gut it. If he fails to do so, which is likely, Trump should issue a covert action finding authorizing the U.S. government to take decisive action. This action would include rendition operations, lethal strikes, and the seizure of cartel assets. The tactical objective should be to significantly weaken the cartel's operations and to eliminate its leadership. The strategic objective should be to send a deterrent message to the other cartels that murdering American citizens is bad for business.

These specific actions must also sit within a broader strategy. Recently praising himself for allowing the cartels' free reign, López Obrador said he was focused on "how to save lives and achieve peace and tranquility in the country using other methods." His shallow wit is now marked not simply with the blood of thousands of Mexicans, but also with the blood of innocent Americans.

The cartels can only be constrained by force. Yes, that constraint requires a much deeper introspection among young Americans as to the costs of their snorting habits. As a country, we should consider drug law reforms that might reduce the street price of illegal drugs and thus reduce cartel profit margins. Nevertheless, American coercive action is necessary.

The example of Colombia proves that it can be done, so let's get on with it.