Question: Who became president in 2015 of the country whose ambassador to the United States from 1910 to 1919 was Rómulo Sebastián Naón? 
Sentence (from "Argentina–United States relations"): Relations have been strained at times over the past few years, especially during the Cristina Fernández de Kirchner administration, but they have improved somewhat since President Mauricio Macri came to power in late 2015.
Relevant evidence: Yes