When the Pentagon suggested in a strategy document last year that the US should be alert to the possibility of a “rapid and sudden collapse” of Mexico as a state, it caused diplomatic heartburn.

While admitting state failure in Mexico was less likely than, say, the collapse of Pakistan, the US Joint Forces Command said Mexico’s government, politicians and judicial infrastructure were under sustained assault from drugs cartels that could trigger a descent into chaos, demanding “an American response based on the serious implications for homeland security alone”.