Good question. Also, one that we can't answer just yet.
For the moment, the center-right Democratic Alliance (AD) has the upper hand with 29,49%, but the Socialists are trailing them by a margin of less than a 1% - roughly 50 thousand votes. It's the lowest winning margin in Portuguese electoral history.
Roughly 1,5 million ballots could still be accounted for - those of the Portuguese voters living in Europe (937 185 voters) and elsewhere (609 345 voters) - so, technically, the Socialists could still win the election - though in the last elections not even 100,000 voters registered abroad exercised their democratic right.
But that's not all: though the Constitution doesn't dictate it, the President typically invites the leader of the most voted party to form a new Government.
Now, some Constitutional Law experts, including Professor Vital Moreira, have argued that this time the President has to take in to account that the AD is a coalition of three parties and not a single party. So, even if the AD ends up winning the largest number of votes, the PS may still be the most voted party in the 2024 legislation, meaning that the President should invite the PS and not the AD to form a Government.
Plus, even if the AD wins, it might still be premature to say that LuÃs Montenegro will be the next Prime Minister of Portugal. Here's why: though it would be an absolute first, the President could ask the current Government to stay on a caretaker role given the tight electoral results, as well as the lack of a working majority in Parliament, until new elections are held - which, according to the Constitution, could not take place before mid-September. So, hold on to your seats - the plot can still thicken.
One thing is for sure: the Socialists' Pedro Nuno Santos will not be the next Prime Minister of Portugal. That's because on the election night he already congratulated LuÃs Montenegro for his electoral victory and conceded defeat, saying that he will lead the opposition and focus on recovering his party's popularity.