The opposition socialists, until now ahead of Portugal's ruling conservative Popular Social Democrats in opinion polls, are in shock after learning some of their senior MPs may be involved in scandal over sex abuse of boys in a state orphanage.
The senior socialist MP Paulo Pedroso, number two in the party and a former labour minister, was taken from parliament by police and held for investigation three weeks ago on 15 counts of suspected child-sex abuse. Eduardo Ferro Rodrigues, the party leader, who is not accused of involvement, testified in court last week, and the former prime minister Antonio Guterres, who is also not under suspicion, visited him in jail to show support.
The abuse accusations centre on Casa Pia, an austere building in a leafy Lisbon neighbourhood, home to children without families, or with parents too poor to care for them. Claims that boys suffered decades of sexual abuse while the authorities did nothing has thrown Portugal into deep shock.
"This is a black moment for us," the veteran commentator Mario Mesquita, a columnist for Publico newspaper, says. "It marks the beginning of a long crisis that's poisoning political life and undermining confidence in our leaders. People were at first incredulous, and are now morbidly pessimistic. This drama shows our dark side, and it's all played out on television, which whips up the frenzy."
Antonio Mega Ferreira, editor of Visao news magazine, says: "I cannot recall, during 25 years of democracy, experiencing such a turbulent, fragile, demoralising, anxious time as we're going through now."
A former home employee, Carlos Silvino, known as Bibi, was detained last autumn accused of abusing children in his care and supplying them for sex to socialites. Among those held on suspicion of abuse are Casa Pia's former director, its doctor, Portugal's favourite television host, a top comedian and a senior diplomat.
Proceedings are still in the investigative stage, with seven suspects detained. More detentions are expected before the trial in September. Adolescents have claimed on television they were offered sweets, ice creams and visits to football matches, then were raped in lavatories or corridors, and recruited for sex parties with powerful "friends". Others, now adult, have told of chilling experiences long suppressed.
Casa Pia came under scrutiny 20 years ago when a young inmate died. He apparently threw himself under a train after running from a car. Officials found the home's doors open all night and youngsters in a cruising area for male prostitutes.
Four children aged between eight and 12, missing for a fortnight, were found in a luxury flat in nearby Cascais owned by a diplomat. They said Mr Silvino had taken them there.
Teresa Costa Macedo, who was the Secretary of State for Family Affairs at the time, ordered a legal investigation that dragged on until it was finally shelved. Mr Silvino was expelled from Casa Pia, then reinstated with back pay in the Nineties.
Rosa Ruela, of Visao, says: "Orphans were considered worthless in Portuguese society then. Child sex abuse was a minor offence, comparable to joyriding. The children were frightened and alone, an easy target. No one took notice of what they said."
Only in the Nineties did Portugal make sex with under-14s a crime punishable by jail; for minors between 14 and 16 the penalty remains a fine. Last September, the mother of an inmate accused Mr Silvino of sexually abusing her son. He was detained in November but insists he is innocent. Last week he indicated he might turn state witness and implicate influential "friends".
In February, counsellors who questioned more than 600 children in Casa Pia found 128 had been abused.
Pedro Strecht, a child psychologist, said "Many wouldn't speak, for fear or shame. We are trained to recognise if children are exaggerating or inventing stories. The testimonies we have heard demonstrate the magnitude of the tragedy."