Recent meetings between Spanish far-right leader Santiago Abascal and members of Mexico’s mainstream opposition have upended politics in Latin America’s second-largest country. Last week, Mr. Abascal, the leader of the nationalistic right-wing Vox party, co-signed an unusually strong-worded letter with members of Mexico’s second and third-largest political groups: the National Action Party (PAN) and the Institutional Revolutionary Party (PRI).
“The communist advance is a serious threat to the prosperity and development of our nations, as well as for the rights and freedoms of our compatriots,” read the document, entitled the Carta de Madrid, or Madrid Letter.
Founded in...