Evidence of The Reconquista
The first evidence comes from the second sentence of their constitution, which states "The faith of the Roman Catholic Church is supported by the state". This is a clear example of Christianity being a dominant religious and political influence due to Spain's Catholicism during the Reconquista.
The second piece of evidence, again from Catholicism, is the current president of Argentina's biography. In it he states he grew up in a Catholic school and learned Christian values there. This shows even more how the government and people of Argentina are dominantly Christian, and how much influence the religion wields over the nation.