the Ballivián government, Siles served as provisional president from 11 April 1952 until 16 April 1952, when Estenssoro returned from exile. The 1951 electoral results were upheld, and Paz Estenssoro became constitutional president of Bolivia with Siles as his vice-president. During the MNR's first 4 years in the office, the government instituted far-reaching reforms, including the establishment of the universal vote, nationalization of the largest mining concerns in the country, and the adoption of a major agrarian reform. In 1956 Estenssoro left the office, as the Bolivian Constitution forbade a sitting president from running for another consecutive term. Siles, his logical successor, easily won the elections of 1956 and became President of the Republic on 6 August 1956. First presidency (1956–1960) The first Siles' administration was more contentious and difficult than revolutionary Estenssoro's had been. During this time MNR began to fragment along personal lines and due to growing disagreements over policy. Economy was in deep trouble, as food and minerals production had plummeted, inflation soared, and the United States conditioned any aid and further support on the adoption of an economic program of its own prescription (the so-called Eder plan) in late 1956 under which Siles accepted USA aid in return for cutting government expenses and social programs. Siles also had to tackle the difficult issue of disarming the worker and miner militia members who had fought in the 1952 Revolution and who had been allowed to keep their weapons. They had served as a useful counterbalance to the possibility of a conservative or military coup against the Revolution, but were by now serving the growing ambitions of the head of the Bolivian Workers' Center (COB) Juan Lechín. Meanwhile, the Falange Socialista Boliviana party schemed to topple the MNR from power, causing a rather disproportionate repressive backlash that diminished MNR's (and Siles') popularity. Break with the MNR and exile, 1960–1978 After the end of Siles' term in 1960, Estenssoro again ran for president in 1960 elections and, upon being elected, sent Siles as ambassador to Uruguay until 1963 and as ambassador to Spain (1963–64). In 1964 Siles broke with Estrassoro over the latter's decision to run for another consecutive term. Siles initially supported the November 1964 coup d'état by vice-president, General René Barrientos and army chief Alfredo Ovando — but was later exiled when it became apparent that the military intended to manipulate 1966 electoral results to perpetuate itself