Italy's centre-left suffered a bitter blow on Friday after its candidate for president, former premier Romano Prodi, came nowhere near securing the necessary votes in a secret parliamentary vote which ended in a fierce rebellion among the bickering parties.
The former European Commission chief, a nemesis of right-wing leader Silvio Berlusconi, had been the front-runner for the job, backed officially by the centre-left.
But the right refused point-blank to support him -- and then over 100 leftist voters broke ranks, leaving him with just 395 votes, well short of the 504 needed to win.
The vote will now go to a fifth round at 0800 GMT Saturday morning, but the uncertainty, broken deals and party betrayals seen so far in each round have dimmed hopes of an end any time soon to a fierce political deadlock in the recession-hit country.
Voting takes place in secret, meaning deputies are not obliged to toe a party line.
Earlier Friday, hundreds of right-wing protesters holding up placards demonstrated in front of the lower house of parliament, chanting "Prodi will not be my president!"
Centre-left leader Pier Luigi Bersani has pinned his hopes on two-time premier Prodi, 73, in a sharp about-turn on an earlier bid to work with the right.
The move, which infuriated his rival Berlusconi, was an attempt to stem the damage caused by the dramatic failure of the Democratic Party (PD) to get their first favoured candidate -- former Senator Franco Marini -- elected after leftist lawmakers rebelled against the choice.
Bersani's decision was scorned by the centre-right, which slammed the bid to crown a man who beat Berlusconi twice in past legislative elections.
"Everything has spun out of control and it doesn't seem there is any candidate who will stick," said political commentator Lina Palmerini in business daily Il Sole 24 Ore.
"What should Bersani do? Better to burn another candidate or resign?" she said.
The PD denied its leader would resign, but experts say the mutiny over the vote risks splitting the party apart -- and that Prodi's candidacy has been blown.
The anti-establishment Five Star Movement, which had also rejected Prodi, said it would continue to support its candidate Stefano Rodota, a human rights advocate and respected academic.
It was not clear who was the front-runner after Prodi's defeat. Party members from across the political sphere were expected to spend the hours before Saturday's vote looking for a new candidate.
Whoever wins will face the challenging task of attempting to unblock an impasse in the eurozone's third largest economy caused by an inconclusive general election in February. Despite numerous willing candidates, the parties have been unable so far to come to an accord.
Prodi's defeat risks toppling Bersani, who has been facing growing calls for his resignation after he threw away a large lead over the centre-right at the general election.
PD rising star Matteo Renzi, mayor of Florence, challenged Bersani for the leadership in December and lost, but many within the party now wonder whether he might have fared better in the elections.
Bersani failed to get enough votes for an overall majority in parliament, with Berlusconi coming a close second and the Five Star Movement led by mercurial comedian Beppe Grillo not far behind.
The three have failed to agree on much over the past two months despite increasingly desperate pleas from big business, trade unions and ordinary Italians as the country endures a painful recession.
Bersani has tried to woo Grillo, to no avail, and has also so far ruled out a "grand coalition" with Berlusconi -- a move that would bring the scandal-tainted billionaire media tycoon back to power.
Observers had been hoping that a cross-party agreement on a new president could yield a broader deal on a new government.
The new president will also have more clout than outgoing President Giorgio Napolitano, who was constitutionally prevented from dissolving parliament and calling fresh elections because he was in the last months of his mandate.
Analysts say the threat of another general election -- an unnerving prospect for financial markets -- could help finally yield a compromise.