A general election was held in Spain on 9 March 2008 to elect the members of the 9th under the Spanish Constitution of 1978. All 350 seats in the Congress of Deputies were up for election, as well as 208 of 264 seats in the Senate. It was held concurrently with a regional election in Andalusia.

The surprise victory of the Spanish Socialist Workers' Party (PSOE) at the 2004 election, amid the public shock caused by the 11M Madrid train bombings, had led to an increase of bipolarization in Spanish politics, with the opposition People's Party (PP) under Mariano Rajoy and right-wing media embracing conspiracy theories about the blasts' authorship and motives while engaging in a strategy of rising tension and street protests against the new government. One of the first measures adopted by Prime Minister José Luis Rodríguez Zapatero was the withdrawal of Spanish troops from Iraq, which caused a downturn in relations with the U.S. administration of George W. Bush. This period saw the implementation of same-sex marriage in Spain, fast-track divorce, measures fostering women's rights and the fight against gender-based violence, as well as the Historical Memory Law recognizing the victims of the Spanish Civil War and the Francoist dictatorship.

Zapatero's decision to engage in talks with the separatist group ETA—after three years of relative calm and a ceasefire in March 2006—was not without controversy, and the government was forced to halt all negotiations following the Madrid–Barajas Airport bombing in December that year. The PSOE government also attempted to enforce a policy of reform of the regional statutes of autonomy, with the issue of the 2006 Catalan statute being the most controversial: its curtailment in the caused the downfall of regional president Pasqual Maragall's cabinet and an appeal to the Constitutional Court being filed by the PP. Although Zapatero's first term saw a continuation of the economic growth of previous years, the growing property bubble in housing prices and a multinational subprime mortgage crisis started showing symptoms of a potential real estate and financial crisis by late 2007.

The electoral outcome saw a record result for both PSOE and PP, which combined amounted for more than 83% of the vote share and 92% of Congress seats. The PSOE benefitted from tactical voting against the PP—at the cost of peripheral nationalist parties, such as Convergence and Union, Republican Left of Catalonia, the Basque Nationalist Party or Chunta Aragonesista, falling to historical lows of popular support—and emerged as the most-voted party just seven seats short of an overall majority, which allowed Zapatero to be sworn in for a second term in office in April 2008. On the other hand, Rajoy's PP saw an increase in its vote share and seat count, but remained unable to overtake the Socialists. United Left had its worst general election performance ever with less than four percent of the share and two seats, whereas the new Union, Progress and Democracy party—founded by former PSOE member and leadership contender Rosa Díez—became the first nationwide party aside from PSOE, PP and IU to secure seats since the Democratic and Social Centre was left out of parliament in 1993.

Background

The 2004 general election was heavily influenced by the Madrid train bombings, seeing the unexpected ousting of the ruling People's Party (PP) amid voters' fury at the crisis' controversial management by the government (accused of a disinformation campaign to prevent the blame on the bombings being linked to the Spanish involvement in the Iraq War). José Luis Rodríguez Zapatero went on to secure investiture as prime minister of Spain with the only opposition of PP lawmakers, subsequently forming a minority government of his Spanish Socialist Workers' Party (PSOE).

Immediately after assuming power, Zapatero's first government fulfilled a campaign pledge to withdraw Spanish troops from Iraq, causing a downturn in relations with the U.S. administration under George W. Bush. Internationally, the country recovered relations with Germany and France and unblocked negotiations for the European Constitution Treaty, which in Spain was successfully submitted to a referendum in February 2005 (albeit amid a high abstention rate). Zapatero also proposed an "Alliance of Civilizations" against Islamist extremism, through increased international, intercultural and interreligious dialogue and cooperation between the Western and Muslim worlds. His government also dealt with the 2007 Morocco–Spain diplomatic conflict over King Juan Carlos I's visit to the cities of Ceuta and Melilla, as well as a diplomatic incident with Venezuela over the King's words "Why don't you shut up?" () directed at Hugo Chávez during the 2007 Ibero-American Summit.

Domestically, Zapatero set out to adopt an ambitious agenda to expand social rights and civil liberties, including the first gender-equal cabinet, measures fostering women's rights and the fight against gender-based violence, the legalization of same-sex marriage, the recognition of long-term care, and the approval of "fast-track" divorce and the first Equality Law, This period also saw the repealing of the Ebro river water transfer, the expansion of anti-smoking bans, the introduction of a point system for driving licenses, the return of the Salamanca Papers to the Catalan government, a new Education Law (the LOE) to improve educational equity and remove compulsory religious classes, an amnesty for migrants working under the table, a €2,500 baby bonus, or a Historical Memory Law to recognize victims of the Spanish Civil War and the Francoist dictatorship. A plan for limited constitutional reform—including the removal of male-preference from the right of succession to the monarchy or a Senate's reform—failed due to a lack of consensus. Immigration remained an issue, particularly with the Cayuco boat crisis that saw over 30,000 illegal immigrants arriving at the Canary Islands by sea in 2006.

Territorial reform became a topic of contention, particularly over the 2006 Catalan Statute of Autonomy (which envisaged a vast expansion of regional powers, of dubious constitutionality). The curtailed the text—following an agreement between Zapatero and Convergence and Union's leader Artur Mas, and in breach of a previous pledge by the former to uphold whatever the Catalan parliament approved—with opposition from Republican Left of Catalonia (ERC) causing the downfall of the Catalan government under Pasqual Maragall; the amended Statute was approved in referendum, albeit under a low voter turnout. A proposed Basque Statute reform to turn that region into an associated state (the Ibarretxe Plan) was rejected by the Spanish parliament in February 2005, prompting the lehendakari, Juan José Ibarretxe, to turn that year's Basque election into a plebiscite on his plan (which ultimately failed). Successful statutory reforms were approved for Andalusia, Aragon, the Balearic Islands, Castile and León and the Valencian Community, with bipartisan support.

The weakening of ETA's activity over continuous police operations prompted the group to back calls for dialogue with Spanish authorities—put forward in late 2004 by its outlawed political-wing, Batasuna—in order to resolve the Basque conflict. Zapatero's government accepted to re-engage in peace talks with ETA, paving the way for a "permanent" ceasefire declaration on 22 March 2006, and the formal start of negotiations in June 2006. Throughout the summer and fall of 2006, the group warned about the peace process being "in crisis" due to the continued police arrests and trials against ETA members, seeing episodes such as member Iñaki de Juana Chaos's hunger strikes or an increase in kale borroka attacks. The 2006 Madrid–Barajas Airport bombing prompted the government to halt all negotiations, with ETA officially ending its ceasefire in June 2007.

The opposition PP under Mariano Rajoy—who succeeded José María Aznar as party leader in October 2004—embraced conspiracy theories about the Madrid bombings' authorship and motives (attributing them as an attempt to "rob" them the election) and, together with right-wing media, engaged in a strategy of rising tension (crispación) and street protests against Zapatero's agenda amid a growing polarization of Spanish politics. Together with the Spanish Episcopal Conference, it opposed reforms on same-sex marriage and education, while it joined the Association of Victims of Terrorism in demostrations against the government's peace talks with ETA (with Rajoy going on to accuse Zapatero of "betraying the dead"). The PP also staged a harsh campaign against the Catalan Statute by tabling a popular initiative (which gathered over four million signatures) and appealing the approved text to the Spanish Constitutional Court, accusing the government of fostering Spain's "breakup". Zapatero remained popular during his first term, seeing his party win the Galician government in the 2005 regional election, and the renewal of the tripartite cabinet (under José Montilla) in the 2006 Catalan election following the Statute crisis. The 2007 local and regional elections were highly bipolarized and globally inconclusive, with both PP and PSOE tying for first place.

The Spanish economy's expansion helped reduce unemployment to record lows since the country's transition to democracy, with the first budget surplus in over three decades, and Spain's GDP per capita briefly overtaking Italy's in 2007 (bringing it close to convergence with the European Union's average). This growth was driven by a real-estate bubble which saw a major rise in housing construction, speculation and rocketing house prices; this, in turn, prompted an increase in the cost of mortgages, and a rise in household debts. Nonetheless, the buoyancy of this period allowed the government to adopt a policy of tax cuts (particularly into lower income and corporate taxes, with more tax deductions) and coin the "cutting taxes is left-wing" slogan. In September 2007, Zapatero boasted about the positive economic figures by proclaiming that, under his government, Spain had "joined the Champions' League of world economies". The outbreak of the subprime mortgage crisis in the United States during the summer of 2007 affected Spain's construction industry and the economy, which started showing signs of slowdown. The squeeze in international credit and looming economic uncertainty switched the political focus during the months previous to the 2008 election, amid a spike in the inflation rate and a rise in unemployment.

Overview Under the 1978 Constitution, the Spanish were conceived as an imperfect bicameral system.. summarizing . The Congress of Deputies held greater legislative power than the Senate, having the ability to grant or withdraw confidence from a prime minister and to override Senate vetoes by an absolute majority.. Nonetheless, the Senate retained a limited number of specific functions—such as ratifying international treaties, authorizing cooperation agreements between autonomous communities, enforcing direct rule, regulating interterritorial compensation funds, and taking part in constitutional amendments and in the appointment of members to the Constitutional Court and the General Council of the Judiciary—which were not subject to override by Congress..

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