In the 1951 elections Paz Estenssoro run for presidency with Siles as his vice-presidential running mate, and won the contest with 42.9% of the vote. However, the ultra-conservative government of Mamerto Urriolagoitía refused to recognize the results and instead turned over the presidency to the commander of the Bolivian army, general Hugo Ballivián. At that point the MNR party went underground and on April 9–11, 1952 led the historic Bolivian National Revolution, aided by defections from the armed forces to the rebel cause (key among which was general Antonio Seleme). Siles played a major role in the revolutionary uprising, along with Juan Lechín, since the MNR leader Paz Estenssoro was at the time in exile in Argentina.