The government declared Salinas the winner, leading to allegations of electoral fraud. The 1997 federal congressional election saw the first opposition Chamber of Deputies ever, and the 2000 elections saw Vicente Fox of a PAN/PVEM alliance become the first opposition candidate to win an election since 1911. This historical defeat was accepted on election night by the PRI in the voice of President Zedillo; while this calmed fears of violence, it also fueled questions about the role of the president in the electoral process and to whom the responsibility of conceding defeat should fall in a democratic election. The role of unions in the new balance of power and future elections is documented in works like historian Enrique Krauze's "Analysis of the Corporative System". After a presidential election, political parties may issue challenges to the election. These challenges are heard by the Electoral Tribunal of the Federal Judicial Power; after it has heard and ruled on them, the Tribunal must either declare the election invalid or certify the results of the elections in accordance to their rulings. Once the Tribunal declares the election valid, it issues a "Certificate of Majority" (Constancia de Mayoría) to the candidate who obtained a plurality. That candidate then becomes President-elect. The final decision is made in September, two months after the election. The 1917 Constitution borrowed heavily from the Constitution of the United States, providing for a clear separation of powers while giving the president wider powers than his American counterpart. For the first 71 years after the enactment of the 1917 Constitution, the president exercised nearly absolute control over the country. Much of this power came from the "de facto" monopoly status of the PRI. As mentioned above, he effectively chose his successor as president by personally nominating the PRI's candidate in the next election. In addition, the unwritten rules of the PRI allowed him to designate party officials and candidates all the way down to the local level. He thus had an important (but not exclusive) influence over the political life of the country (part of his power had to be shared with unions and other groups, but as an individual, he had no peers). This and his constitutional powers made some political commentators describe the president as a six-year dictator, and to call this system an "imperial presidency". The situation remained largely unchanged until the early 1980s when a grave economic crisis created discomfort both in the population and inside the party, and the president's power was no longer absolute but still impressive. An important characteristic of this system is that the new president was effectively chosen by the old one (since the PRI candidate was assured of election) but once he assumed power, the old one lost all power and influence ("no reelection" is a cornerstone of Mexican politics).