A substantial pool of voters is still undecided. The country's traditional parties have been diluted. And a rising populist party has splintered the right.
The ballot will be Spain's third parliamentary election in less than four years, with no sign that the uncertainty will go away anytime soon.
Socialist Prime Minister Pedro Sánchez is hoping voters give him a strong mandate to stay in the office he assumed 11 months ago, when a no-confidence vote ousted his conservative predecessor. However, about a third of those surveyed heading into the final week of campaigning said they didn't know how they would cast their votes.
The upstart Vox party seems sure to garner enough support to put far-right lawmakers in Spain's lower house, the Congress of Deputies, for the first time since the 1980s. A strong performance by Vox would be crucial to the ability of two center-right parties to forge a majority coalition government to supplant Sánchez.
Sánchez urged voters who abandoned the Socialists in recent years to once again vote for Spain's oldest national party "so that we can stop the three parties on the right from joining forces."
If Vox does as well as expected, Spain would have five national parties of significant size. A government opinion poll of 16,194 eligible voters forecast that Sánchez*s Socialists would win 30% of the vote, the conservative Popular Party 17%, the center-right Citizens 13%, the far-left United We Can 12% and Vox 11%.
All the polls published by private news organizations in Spain also forecast Sánchez leading the Socialists to victory for the first time since 2008.
"We are very close to seeing the Socialist party winning an election 11 years since its last victory," Sánchez said. "We are very close to being able to offer all Spaniards a prospect of stability, of a country that is walking toward a future of more social justice, more peaceful coexistence and a clean manner of doing politics."
In 2008, the Socialists and their ideological rivals from the Popular Party together accounted for 82% of the vote. The combined vote total for the two parties, which dominated Spanish politics for three decades, fell to 50% in the December 2015 election. In the period in between, the global economic meltdown hit Spain hard and helped give rise to the Citizens party and United We Can.
The fragmentation has made the governments in Madrid much more fragile and short-lived.
The current Socialist-led government and the one the Popular Party led from 2016-2018 controlled a minority of parliament seats. Neither accomplished much or came close to seeing out a full four-year legislative term. Sánchez was forced to call this weekend's early election after he was unable to get a national budget passed in February.
"For the foreseeable future in Spain, parties are going to have to establish agreements," said Andrew Dowling, an expert on contemporary Spanish politics at Cardiff University in Wales. "I don't think there's any indication any single party will be able to win. We should remind ourselves that as late as 2004 and 2008, the Socialists were able to get 42 percent of the vote. They're a long way from going back there."
Two nights of televised debates gave the candidates ample time to trade barbs and to try to win over undecided voters. But before the election, there's been more talk about postelection partnerships than about policy platforms.
Pablo Iglesias, the leader of United We Can, was lauded for his moderate tone and defense of the Spanish Constitution during one of the debates, a contrast to his fiery, revolutionary rhetoric during past campaigns. Iglesias has talked openly of wanting to come into government with the Socialists.
Sánchez's ideal scenario would be to cobble together reliable support from 176 of the 350 members of the Congress of Deputies through his Socialists, Iglesias* United We Can and moderate regional lawmakers from the northern Basque Country.
If he can't build a majority that way, Sánchez might find himself again relying on pro-independence lawmakers from the Catalonia region who already proved to be untrustworthy partners. Catalan separatists in parliament voted against the prime minister's national spending bill after Sánchez refused to authorize a referendum on the region's secession from Spain.
The chance of Popular Party leader Pablo Casado becoming prime minister rests on his candidates beating hopefuls from Citizens and then striking a deal with the center-right party to form a coalition government. If Vox representatives agree to support the coalition, the Popular-Citizens government would be able to command a majority of votes in parliament.
Casado, Citizens leader Albert Rivera and Vox leader Santiago Abascal have competed to be seen as tough enough to stand up to the separatist politicians in Catalonia. A failed push to declare the region's independence in 2017 plunged Spain into a deep political crisis.
All three right-wing parties - Popular, Citizens and Vox - accuse Sánchez of being weak on Catalonia because he opened talks with the region's pro-secession leaders.
The three parties came together to defeat Sanchez's Socialists during a December election in southern Spain's Andalusia region, long a Socialist stronghold. The Andalusia election introduced Vox to the Spanish political scene. The party campaigned on stemming illegal immigration, protecting Spanish traditions like bullfighting and vows to punish Catalonia by taking over its regional government.
Now the three are competing to see which of them could lead a similar takeover at the national level.
"I think what Sunday will decide is who is the winner on the right," Dowling said. "It will be very much a kind of a choice between head and heart for right-wing voters."
Aritz Parra contributed to this report from Madrid.
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