In a new twist, Mexicans who in the past resisted the idea of American “boots on the ground” to aid their country’s fight against crime cartels are now increasingly open to it, The New York Sun has learned. President Trump, in contrast, is launching a tariff battle against the southern neighbor, citing the flow of fentanyl.  

America could significantly beef up the presence in Mexico of agents from the Drug Enforcement Agency and the CIA, a former Mexican foreign minister, Jorge Castaneda, tells the Sun: “You can certainly see more U.S. boots on the ground, although not necessarily military boots.” 

While there are American military representatives in Mexico for training purposes, a more substantial presence could be politically and legally complicated, Mr. Castaneda says. Yet Mexico is being rocked by deadly cartel wars, and there is a growing recognition that America could aid in the battle against the crime lords.     

President Sheinbaum, the Mexican leader, had previously spoken passionately against American intervention in the country’s battle against the cartels. Now, though, she is changing her tune. “We all want to combat the drug cartels, that is evident,” she said Tuesday. “So what does one have to do? One has to join forces, collaborate” with America. 

Mr. Trump issued an executive order this week to designate the Mexican cartels as foreign terrorist organizations. Such a designation could trigger aggressive measures. As yet, though, such measures are being directed at Mexico, not the cartels. Press Secretary Karoline Leavitt confirmed on Friday that 25 percent tariffs will be imposed on Mexico and Canada, and 10 percent on Communist China. 

Ms. Leavitt said that the measures are in retaliation for “the illegal fentanyl that they have sourced and allowed to distribute into our country.” Mr. Trump has made the fight against illegal migration and the flow of drugs central to his second term’s policies.

The newly imposed sanctions could force Ms. Sheinbaum to deepen cooperation with America. Yet, Mr. Castaneda says, “she’s been in office now for four months, and three months have passed since the U.S. election. And from what we know, they haven’t talked about any of these things.” 

As Secretary Rubio launches a Latin America trip next week, he is making a point that the Western Hemisphere will be central to Mr. Trump’s foreign policy. It is the first time “in over a hundred years” that a secretary of state is making his first trip abroad to Latin America, the department’s special envoy to the region, Mauricio Claver-Carone, told reporters Friday.

The “last time that happened, I believe, was in 1912, when Philander Chase Knox went to Panama” to watch the conclusion of the canal’s construction, Mr. Claver-Carone added. Panama will be Mr. Rubio’s first stop, followed by El Salvador, Guatemala, Costa Rica, and the Dominican Republic. 

Mr. Trump has made “America first” central to his presidency, and “in the realm of diplomacy, this means paying closer attention to our own neighborhood—the Western Hemisphere,” Mr. Rubio writes in the Wall Street Journal, previewing the trip.

One issue the secretary could bring up with President Mulino of Panama next week is the Islamic Republic of Iran’s use of Panamanian-flagged ships to smuggle arms and cash to proxies and illicitly export oil to its allies, the United Against Nuclear Iran chairman, Jeb Bush, and its CEO, Mark Wallace, write.

“We call on Panama to immediately and verifiably confirm that it will de-flag all ships identified by UANI as part of the ‘Ghost Armada,’” they write. “We also call on Panama to cease and desist from flagging all vessels smuggling Iranian energy products in the future.”

While he is set to visit Panama and other small Latin powers, though, Mr. Rubio is skipping the region’s top powerhouses, including America-skeptic Brazil and tightly allied Argentina. While well aware that Mexico is crucial to realizing much of Mr. Trump’s agenda, Mexico City is also not included in the secretary’s trip.    

In Mexico, the cartels “are the most powerful force on the ground, and they are plowing into the United States,” Mr. Rubio said on “The Megyn Kelly Show” on Friday. “They’re facilitating illegal migration, but they are also bringing in fentanyl and deadly drugs to our country. “

Such activities, he added, “are a national security threat and that needs to stop. So we expect their cooperation on that, because they should. If it was the other way around, they would expect that as well. And that needs to be addressed.”

While Mr. Rubio on Thursday had a sit-down with Canada’s foreign minister, Melanie Joy, he is yet to meet his Mexican counterpart, Juan Ramon de la Fuente, or invite him to Washington. 

Messrs. Rubio and de la Fuente exchanged pleasantries on the phone last week, according to Ms. Sheinbaum. If America is to utilize Mexico’s new openness to cooperate on the cartel wars, though, Mr. Rubio could benefit from more substantial cooperation.