Voters in Portugal have gone to the polls, in an election that will either keep the centre-left in power or shift the country to the right.
Opinion polls suggest neither the Socialists nor the opposition centre-right is likely to win outright.
This could leave the far-right Chega party as kingmaker, although mainstream rivals have vowed to sideline it.
Turnout by 16:00 GMT was just under 52%, already higher than the total turnout in the last vote in 2022.
Exit polls were due to be released at 20:00 GMT, an hour after voting ended in mainland Portugal.
Mr Costa was not named as a suspect, but investigators arrested his chief of staff over alleged irregularities in state contracts.
Despite economic growth under the Socialists, Portuguese voters worry about high inflation, deteriorating public services, and a housing crisis.
Mr Ventura, a former centre-right councillor and one-time trainee priest, made his name on national television as a football commentator.
He has called for dramatic policy shifts, and under his leadership Chega won 7% of the vote in the 2022 legislative elections.
Polls suggest that it could now double this score, leaving it potentially able to keep a minority centre-right government in power – at a price.
The leader of the centre-right Democratic Alliance, Luís Montenegro, has said he would not seek Chega’s support for his programme of tax cuts and free-market reforms.
The Socialists are led by Pedro Nuno Santos, a former minister under Mr Costa, who has defended the outgoing government’s record.
In eight years of Socialist rule, unemployment has dropped and the economy grew by 2.3% last year.
A total of 10.8 million people are registered to vote in the elections to choose 230 members of parliament.