Suddenly, New York's Mr Morality has a lot of explaining to do (and not just to his wife)

When Hillary Rodham Clinton confirmed a few months ago that she was indeed going to run in New York state for a seat in the US Senate, she insisted on one thing: the contest would be about the issues, not about personalities. Tell us another one, we thought. This will be about you, your husband and your marriage.

We were all wrong. As tantalising as it was to watch the First Lady depart the White House this winter and settle alone in the leafy New York suburb of Chappaqua, it hardly prepared us for what we have now. That is the public unravelling of the man she is meant to be running against, Rudolph Giuliani. In fact, so complete and astonishing are the disasters now besetting him, he may soon be forced to withdraw.

When Mr Giuliani, the Mayor of New York City, told reporters on Wednesday that he was seeking a legal separation from his wife of 16 years, Donna Hanover, and thereby essentially confirmed what had been rumoured for years - that he had been cheating on her - it was as if a political bomb had gone off. Yesterday, the debris was still falling as voters and party strategists struggled to take it all in.

Husbands and wives part. But things are different when a public leader is involved, especially if that leader, as in Mr Giuliani's case, is a Republican famous for self-righteous moralising. This is the same mayor who tried last autumn to close down Sensation, an exhibition in Brooklyn of art by young British artists, because he was offended by a work depicting the Virgin Mary clad with elephant dung.

And there is simply the tragicomic manner in which this particular domestic débâcle has unfolded. Truly, it has been the stuff of your most cheesy daytime soap.

Cast your mind back two weeks to that other blockbuster episode of The Rudy Chronicles, when he revealed that he had treatable prostate cancer.

The next story twist began to surface a week ago, when a New York tabloid published pictures of the Mayor leaving a restaurant with a woman identified as Judith Nathan, an Upper East Side divorcee and mother. The paper made clear its view that the two were having an affair, and, indeed, were inseparable. Rudy, apparently, was taking her to public events and spending weekends on Long Island with her.

Mr Giuliani responded by acknowledging only that he and Ms Nathan were "very good friends". In the meantime, Ms Hanover made a statement of her own, saying that her marriage to Rudy remained "precious". She also said she was pulling out of an engagement to appear in a controversial Broadway production, called The Vagina Monologues, to be able to concentrate on her husband's cancer crisis.

Then Wednesday happened. "For quite some time, it's probably been apparent that Donna and I lead in most ways independent and separate lives," a visibly distraught Mayor confessed. "It's been a very painful road and I hope we'll be able to formalise that in an agreement that protects our children".

Barely had the body politic of the city caught its breath when Ms Hanover, who is an accomplished journalist and actress, was behind a microphone outside the mayoral home, Gracie Mansion. Similarly shaken, she expressed her sadness about the turn of events. Then she let her husband have it.

The marriage, she let us all know, had been violated long before the Mayor took up with Ms Nathan. For years before that relationship he had been entangled with a "staff member" of his office. A spokesman for Ms Hanover later identified that person as his former spokeswoman, Cristyne Lategano.

"I had hoped to keep this marriage together," Ms Hanover said. "For several years it was difficult to participate in Rudy's public life because of his relationship with one staff member. Beginning last May, I made a major effort to bring us back together. Rudy and I re-established some of our personal intimacy through the fall. At that point, he chose a different path."

So can Mr Giuliani carry on with his campaign? This is the question the entire state - and the entire hierarchy of a now very jittery Republican Party - now wants answered.

The cancer issue alone was enough to cast it in doubt. Mr Giuliani, who is 55, said after announcing his diagnosis that he would make up his mind before the end of the month, depending on what his doctors tell him about treatment. Officially, that remains the position. And officially, the turmoil in his romantic life will not be a consideration.

In the minutes following the Mayor's statement, political observers and Republican insiders remained mostly convinced that he could still be a viable opponent to Mrs Clinton, his cancer allowing. But after Ms Hanover let off her artillery rounds, opinions were decidedly more mixed.

The information about the Mayor and Ms Lategano may prove especially damaging. When Vanity Fair reported in 1997 that the relationship between them was more than just professional, both of them vehemently denied it. The Mayor, it seems, has therefore been caught in a lie and with his pants down, just as President Bill Clinton was in the Monica Lewinsky scandal.

Questions will doubtless also be asked about possible favouritism towards Ms Lategano. Not long after the Vanity Fair article, she left the Mayor's office and turned up as head of the taxpayer-funded New York Convention and Visitors Bureau. A large sum was paid to her predecessor to step aside. Ms Lategano now draws a salary of $150,000.

After leading the First Lady through all of the winter, the Mayor is now marginally behind her in the latest statewide polls. His numbers suffered most in the days after the accidental shooting by police in March of another unarmed African American in the city, Patrick Dorismond. The Mayor drew furious criticism when he unsealed juvenile criminal records on Dorismond, apparently to sully his name. With the race so tight, his marital problems are likely to matter, especially with upstate voters, as well as conservative Catholics and Jews in New York City.

A former US Senator from the state and a Republican, Alfonse D'Amato, said he thought it might be over for Mr Giuliani. "For the first time, I really wouldn't be surprised if Rudy doesn't run," he conceded.

"He's got to get out," one Republican insider remarked with evident exasperation. "I don't understand why he's doing it in a five-act opera. Maybe he just likes opera."

Others in the party argue that if President Clinton was able to survive Monicagate, then surely Mr Giuliani could conquer all this.

Already, however, the party is having to scramble to prepare possible alternatives to run in Mr Giuliani's place. The names being talked about are Rick Lazio, a Republican congressman from Long Island, and Theodore Forstmann, a wealthy, but little-known, Wall Street financier.

How much longer will it be, meanwhile, before we start talking about Hillary again?

For now, she is saying as little as possible about Rudy and his tribulations. Why should she? She knows only that the prize she wants more than any other - a seat in the US Senate, from which, one day, she may even hope to launch a bid for the presidency - is a little bit closer to her grasp than it was just two days ago.