Texas governor and presidential candidate Rick Perry is floating the idea of invading Mexico. Too late: the U.S. military is already up to epaulets there.

“It may require our military, in Mexico, working in concert with them, to kill these drug cartels and to keep them off our border and to destroy their networks,” Perry said during a campaign stop in New Hampshire on Saturday, reported the Dallas Morning News. “It is very important for us to work with them to keep that country from failing,” he added.

Mexico’s ambassador to the U.S., Arturo Sarukhan, was skeptical of Perry’s offer. Sarukhan told the Morning News the U.S. and Mexico share “a new paradigm of joint responsibility, law-enforcement, security and intelligence cooperation” aimed at confronting the cartels. “But U.S. boots on the ground in Mexico is not in the books; it is a non-starter.”

The ambassador isn’t kidding about joint responsibility. Defense and intelligence cooperation is a crucial — and growing — feature of U.S.-Mexico relations. First, there is the “unprecedented” $1.6 billion (total) Merida Initiative, which trains Mexican cops and provides U.S. equipment ranging from UH-60 Black Hawk and Bell 412 Enhanced Performance helicopters to telecommunications gear.

Second, the Mexican government confirmed in March that unarmed U.S. drones were operating inside the country under Mexican supervision. The Mexican government was also revealed to have launched counter-drug operations from within U.S. territory. And in November of last year, Mexico’s Proceso exposed a secret base near the U.S. embassy in Mexico City, possibly housing a buffet of Washington’s top intelligence, defense and law enforcement agencies.

But boots on the ground? Unless Perry is cooking up a second Punitive Expedition, the odds of a direct military presence is remote, at best. Currently, the Mexican government won’t even allow U.S. law enforcement to piggyback on operations, let alone carry personal arms. This doesn’t mean, however, there are no other — let’s say — creative ways of assisting the Mexican government.

According to a New York Times report in August, the U.S. sent a small team of CIA agents and “retired military personnel” to collaborate with Mexican police from inside an undisclosed military base. Not only that, the Times report notes the U.S. is considering embedding mercenaries within an elite Mexican police unit. Mexican law may restrict agents of foreign powers from operating within the country, but it’s a different matter for private contractors and retired veterans.

It’s also a reflection of “serious constraints on U.S. influence” in Mexico, noted U.S. Army War College Professor George W. Grayson, “largely because of the reactive nationalism that infuses Mexico’s political, media, and academic sectors, not to mention traditionalists in Mexico’s Ministry of Defense who resent being tutored by North Americans, no matter how diplomatic and well-meaning the instructor.”

In other words: For now, don’t expect any American troops to march across the Rio Grande. The U.S. will stick to drones and cash and covert agents and mercenaries — just like it’s doing in Mexico, already.