But as a matter of principle, the U.S. demand that Mexico sign a safe-third-country agreement is stronger than it looks. It’s not just that Mexican authorities often look the other way — or even provide assistance — as hundreds of thousands of foreigners pass through its territory on the way north. Rather, the possibility of asylum in the U.S. serves as way for Mexico to avoid the consequences of its own very expansive asylum laws.

Mexico is a signatory to the 1951 Convention (and the 1967 Protocol, which expanded the refugee treaty from just Europe to the whole world). Under that treaty, the definition of a refugee is anyone outside his country who is unwilling to return because of a “well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion.” This definition has been added to U.S. law.

In addition, though, Mexico joined a number of other Latin American countries to sign the 1984 Cartagena Declaration on Refugees. That declaration significantly expands the definition of a refugee to include “persons who have fled their country because their lives, security or freedom have been threatened by generalized violence, foreign aggression, internal conflicts, massive violation of human rights or other circumstances which have seriously disturbed public order.” This standard, which has been formally incorporated into Mexican refugee law, is so broad as to extend asylum protections to hundreds of millions, potentially billions, of additional people.