The horrific murder of three American women and six of their children in northern Mexico this week awoke many in Washington to the continuing deterioration of security conditions south of the border. To Mexicans, it was only the latest in a string of shocking episodes.

The ambush of fundamentalist Mormon families in a desolate stretch of desert followed by just a few weeks the siege of a medium-size city, Culiacán, by hundreds of drug cartel fighters who outgunned Mexican security forces to release a cartel leader they had tried to arrest. Just days before that, 14 police officers were gunned down during an ambush in the state of Michoacan. And before that, the firebombing of a club in Veracruz killed at least 27 people. And so on.

Mexico has struggled for years with the mayhem sown by drug cartels, but there has been an alarming escalation since leftist President Andrés Manuel López Obrador took office last December. In the first six months of 2019, there were some 17,000 homicides, and it seems likely the total for the year will surpass last year's total of 33,000, which was the most ever recorded.

It's hard not to conclude that the spike is a consequence of López Obrador's policy of deescalating the war on the cartels waged by previous presidents, which he labeled "a disaster." His catchphrase has been "hugs, not bullets"; he says more social spending and the weeding out of corruption in government will reduce the violence. Following the slaughter of the Americans, the president was defiant: "You can't fight violence with more violence," he said.

López Obrador has a point in arguing that the previous strategy of mobilizing the military against the cartels failed to defeat them while causing thousands of casualties. His own approach is not as pacific as it sounds: He created a 60,000-strong national guard to take up the fight. But the guard is distributed thinly around the country, and a chunk of it has been diverted to stopping migrants from Central America, in an effort to appease the Trump administration.

López Obrador may calculate that the easiest way to reduce violence is to back off and hope for a de facto truce with the gangs. The massacre of the Mormons shows why that won't work: As the drugrunners fight each other or prey on legitimate commerce, innocent people are killed.

What Mexico needs is a comprehensive approach to fighting the cartels that includes more social spending but also more and better-equipped security forces, and an improved justice system. The United States, which for years has partnered with Mexico in counter-narcotics, could do much to help. Unfortunately, President Donald Trump's approach to the problem amounts to empty rhetoric: "This is the time for Mexico, with the help of the United States, to wage WAR on the drug cartels and wipe them off the face of the earth," he tweeted recently.

As Mexico has painfully learned, it's not as simple as that. López Obrador needs to adjust his strategy. But Mexico is unlikely to quash the cartels until it can partner with a U.S. president prepared to do more than posture.

This editorial is the opinion of The Washington Post's editorial board.