Portuguese voters will elect a new parliament on Sunday, facing a choice between switching to a centre-right government or keeping the centre-left in power, although neither appears to have a clear path to a full majority as the far-right's clout grows.
The early election, four months after Prime Minister Antonio Costa's sudden resignation amid a graft investigation, again pits against each other the two centrist parties that have alternated in power since the end of a dictatorship five decades ago.
The ruling Socialist Party (PS) could attempt a replay of their old alliances with the Left Bloc and the Communists that allowed them to govern between 2015 and 2019, if the combined left gets more than 115 seats in the 230-seat parliament.
The Democratic Alliance (AD) of right-leaning parties, helmed by Luis Montenegro, leads in most opinion polls, but it could struggle to govern without the votes of far-right Chega. Montenegro has so far ruled out any deals with the radical populists, who want a government role.
Surveys suggest support for Chega's anti-establishment message, its vows to sweep away corruption and hostility to what it sees as "excessive" immigration, has roughly doubled since the last election in 2022, though it remains in third place.
On Friday, conservative President Marcelo Rebelo de Sousa told Expresso newspaper he would do everything he can to prevent Chega from gaining power, drawing criticism as the head of state is mandated to remain neutral.
Political scientist Antonio Costa Pinto of Lisbon University said Portugal "has entered the dynamic of many European democracies", in which the centre-right is challenged by having a radical party to its right consolidated in third place.
A potential AD minority government, even supported by the smaller centre-right Liberal Initiative, would likely need votes from Chega to pass legislation, making it relatively fragile as Chega could topple it at any point.
However, "a PS victory with an absolute right-wing majority in parliament would be the most complex, most unstable scenario," Costa Pinto added.
Polls open at 8 a.m. (0800 GMT) and close at 7 p.m. in the mainland and an hour later on the Azores archipelago. More than 10 million citizens are eligible to vote.
