LUKEVILLE, Ariz. — Each year, Mexican drug cartels rake in billions of dollars in profits from the sale of heroin, methamphetamines and other drugs in the United States. The money has to make its way south somehow.

Though the cartels sometimes hire legitimate companies to buy goods like silk and ink cartridges and export them to Mexico, where they are sold for pesos, a more common method is to simply pay someone to drive the cash over the border.

President Trump has talked frequently about “bad hombres” streaming in from Mexico. But it is the flow of money going from north to south — a product of Americans’ voracious appetite for illicit drugs — that officials say is an equal part of the problem.

“It’s the money and the guns that have enabled the cartels to obtain the power they have,” Scott Brown, special agent in charge of Homeland Security Investigations in Phoenix, part of Immigration and Customs Enforcement, said in an interview. “I’m a firm believer that if we can keep the cartels from getting their profits, over time, that has a lot more impact than seizing the drugs.”