At 9.30pm last night, a few dozen activists gathered at the James Joyce bridge in Dublin. They wanted, they said, to see the sun set for the last time on the Eighth Amendment to the Irish constitution, which was passed into law in 1983. It reads: “The state acknowledges the right to life of the unborn and, with due regard to the equal right to life of the mother, guarantees in its laws to respect, and as far as practicable, by its laws to defend and vindicate that right.”

The campaign to repeal the amendment has pointed to the cruelty of this approach in practice. Even a foetus which cannot survive – perhaps because of a developmental abnormality – must be “protected” until the heartbeat stops. The life of its mother can be forfeit as a result. Unlike in almost every other country in the developed world, pregnant Irish women cannot be sure that their safety will be put first if they need medical attention.

In 2012, a 31-year-old dentist called Savita Halappanavar died from sepsis after her waters broke but hospital staff refused to give her drugs to accelerate the delivery, citing the Eighth Amendment. Both her father, Andanappa Yalagi, and the chair of the inquiry into her death, Prof Sir Sabaratnam Arulkumaran, have backed a Yes vote in the referendum.

Here in Dublin, Savita’s face is everywhere. To the Yes campaign, she is a symbol of the hollowness of anti-abortion campaigners’ claims to be “pro-life”. Where is the care for women’s lives, for their hopes, their dignity, their safety? But the lamp-posts are busy, crowded with No posters too. Voters are urged to “save lives”, to “love both”. Pictures of foetuses abound, with messages about when their hearts start beating. In a rhetorical flourish the Yes campaign say is imported from America, anti-abortion posters sometimes refer not to the “unborn” but to the “preborn”.

The involvement of the well-funded US pro-life movement is an open question, and a victory for No will prompt soul-searching about interference with the vote. It is notable that both Google and Facebook, in the run-up to polling day, imposed restrictions on adverts related to the referendum. But will we ever know who spent what, and the effect it had? The experience of both the EU referendum and the US presidential election suggests that uncovering the mere facts is hard enough. Trying to quantify the influence of “dark ads” and targeted posts is even harder.

The experience of the votes for Brexit and Trump – which shocked and horrified progressives who had become used to things going their way – hangs heavily in the background here. The REPEAL jumpers – slabby white letters on a black sweatshirt – have become iconic, and on the commuter train from Tara Street to Dun Laoghaire yesterday, both young men and young women wore badges saying “Yes” – or its Gaelic equivalent, “Tá”. But everyone expects that “Shy Nos” are a greater force than the streets or social media would lead you to expect.

Even in the suburbs of Dublin, the most optimistic prediction I heard was a Yes win of 55-45 per cent. (“There are some men that feel beleaguered, like women are running away with it,” I was told.) A woman I know who has been canvassing for Yes in rural Donegal – which only narrowly voted for gay marriage in 2015 – was despondent about the chances of victory the last time we spoke. Even on the march to James Joyce bridge I found women who expected the vote to be lost. (I also saw tweets from people who didn’t want to go at all, feeling that it was tempting fate.) It’s hard to know whether this is just sensible caution or the scent of something wrong.

Even a narrow victory would bring problems. A Yes vote would merely repeal the constitutional amendment; new legislation to decriminalize abortion would be needed afterwards. To the No campaign, England is a warning – posters here in Dublin claim that one in five English pregnancies end in abortion. The most anyone is talking about for Ireland is a time limit of 12 weeks, and even that will be fiercely resisted. (One of the most unexpected conversations I had yesterday was with a Yes canvasser, who told me that the English time limit of 24 weeks made her very uncomfortable.)

The campaign itself has been divisive and occasionally bitter; for a generation of activists, it will be a defining experience, whatever the result. "I've been shouted at, spat at, called a baby murderer," Lisa Wilkinson, director of the Elbow Room and organiser of the rally, told me on the way to the river. "But we've tried to keep it positive."

Until polls close, there is now a broadcast media blackout; an exit poll is expected at 11.30pm. The results themselves are due in the early afternoon. Only then will we know if all those campaigners, tired but hopeful, on James Joyce Bridge really did watch the sun set on the Eighth Amendment for the last time.