His fall formally opened a leadership crisis which could lead to a split or even the destruction of his century-old party. This in turn could bring down the fragile coalition of Giuliano Amato, the Prime Minister.
The government almost capsized itself, already badly hit by the resignation of the Justice Minister, Claudio Martelli, Mr Craxi's main rival in the party, and by rumours - denied by public prosecutors - that Mr Amato was under investigation.
The President, Oscar Luigi Scalfaro, backed the government, saying it was unthinkable that it should go. The Prime Minister promised urgent measures to clean up the scandal-ridden political system, because 'the credibility of our government, parliament, our industrial system and our ability to compete abroad are at stake'.
He said there would be strict controls on the civil service and a new code of ethics for politicians, and urged electoral reform, which is bogged down in parliament.
Mr Craxi had long been under pressure to resign from his post in the party which he had led to great successes over the past 16 years, ever since his political associates in Milan became embroiled in the big corruption scandals there, and because he was seen as the main obstacle to a clean-up and rehabilitation of the party which was urgently needed for it to survive.
With six judicial investigations opened against him on suspicion of corruption, extortion and fraudulent bankruptcy, he could no longer cling to the job. He is nevertheless claiming it is a plot to destroy him, while blaming the rest of Italy's political leadership.
In recent months Mr Craxi became the symbol of all that is wrong with Italian politics. But it was not always thus.
Energetic, decisive, cunning, aggressive and supremely self-confident, his personality outshone the grey leaders of the Christian Democrats with their compromises and political immobility.
One admirer once described him as a 'cock among capons'. He took over a party that was in danger of being crushed between the Christian Democrats and Communists and took its share of the vote from 9 to 16 per cent.
He later served as prime minister from 1983 to 1987, Italy's most economically buoyant and self-confident years.
What few realised then was that his party had adopted the Christian Democrat habit of taking rake-offs on public works contracts and often surpassed them in brazenness and greed. It was all tacitly accepted and no one dreamt that they would ever have to pay for it. Now the bills are coming in.
The Socialist Party's national assembly is due to meet today to elect a successor, with no obvious candidate in sight.
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