Complex sentence: Members of his party chose him as the PAN presidential candidate in a series of three primary elections, he defeated the favored former Secretary of the Interior under President Vicente Fox, and thus the election of Calderón as party candidate surprised many analysts.
Split into simpler sentences: Members of his party chose him as the PAN presidential candidate. In a series of three primary elections, he defeated the favored former Secretary of the Interior under President Vicente Fox, and thus the election of Calderón as party candidate surprised many analysts.