Tonight it is the Republicans’ turn to face questions from YouTubers, the novelty debate format that, if the Democrats’ experience is anything to go by, adds little more than bad homemade mini-movies to the usual platitudes and obfuscations from the stage.

Because Senator Clinton appears to have a lock on the Democratic nomination, notwithstanding Senator Obama’s statistical tie in Iowa, the Republican race is turning out to be the more interesting and the more capable of springing surprises.

The jousting between Mayor Giuliani and Governor Romney these last few days is because both have emerged as the simultaneous front runners. In national polls, Mayor Giuliani has a generous lead, spurred by his claim that he and he alone can beat Mrs. Clinton in November.

Governor Romney, meanwhile, has established himself at the top of the polls in Iowa and New Hampshire, thanks to the generosity of his donors, notably himself, who have pumped $20 million and more into television advertisements in these early states.

Until recently, the mayor affected to play down the importance of Iowa and New Hampshire, arguing that his personal strategy for reaching the White House meant traveling a very different route to the rest of the field because, as a liberal northeasterner, he was uniquely equipped to win votes in New York, Florida, and California.

More recently, however, he appears to sense a weakness in Governor Romney’s support in New Hampshire, where the voters have established a long standing preference for maverick tough guys like Mr. Giuliani over smooth operators like Mr. Romney.

In his recent visit to New Hampshire, Mr. Giuliani has been raising an issue on which he believes himself to be strong and Mr. Romney weak: law and order. What is more, Mr. Giuliani believes he has found his own Willie Horton. It was the wretched murderous Horton, you may remember, who reduced to nil the presidential chances of another former Massachusetts governor, Michael Dukakis, a Democrat.

In brief, Horton was a convicted killer who tortured and raped a Maryland woman while enjoying a weekend pass from a Massachusetts prison in 1987. Mr. Dukakis, a Massachusetts liberal, was in favor of the more lax approach to offenders which freed Horton to commit acts of torture and rape, and, as governor at the time the crimes took place, he was blamed for the incident.

Horton’s spree was not the only thing to ditch Mr. Dukakis’s chance of reaching the White House, but the beauty of the story — weak, well meaning, but ultimately gullible governor frees a hardened criminal to strike again — was its simplicity. Mr. Dukakis’s rival, George H.W. Bush, made a single devastating campaign advertisement which simply showed a prisoner passing through a revolving door.

Mr. Giuliani’s own Willie Horton, Daniel Tavares, spent 16 years in Massachusetts prisons for stabbing his own mother to death in 1991. While behind bars he threatened the life of Governor Romney and repeatedly fought with prison guards. On his release in June this year, Tavares was promptly rearrested for the assaults on the guards.

The following month, Massachusetts Superior Court Judge Kathe Tuttman, who was appointed by Mr. Romney in April 2006, stepped in, overturning two $50,000 bail orders imposed on the killer, and releasing him on condition that he live with his sister in Massachusetts, work in the state, and call his probation officers three times a week.

This month, Tavares was rearrested in Washington state on a new charge: that he killed a newly married young couple, Brian and Beverly Mauck, in an argument over $50.

Again, the story, as told by Mr. Giuliani’s people, is a simple one: a weak, well meaning, but ultimately gullible governor appoints a liberal judge who frees a hardened killer to strike again. For Mr. Giuliani, a top flight prosecutor, it was all too easy to broaden the attack u p o n Mr. Romney’s general competence.

“The governor is going to have to explain his appointment, and the judge is going to have to explain her decision, but it’s not an isolated situation,” Mr. Giuliani told reporters. “Governor Romney did not have a good record in dealing with violent crime.”

You may expect to hear some reference to Daniel Tavares and his criminal career in tonight’s televised debate and it will be fascinating to see how Mr. Romney wriggles.

The governor can claim, with justification, that he appointed Kathe Tuttman, a former prosecutor, because of her supposed toughness. He can point out that he has demanded her immediate resignation, though he did so without the precaution of calling for a full investigation or talking to her.

He can insist that crime in Massachusetts fell over the time he was governor, though Mr. Giuliani’s campaigners are already issuing figures showing the governor presided over “an increase in murder and violent crime.”

Like Mr. Dukakis, the problem Mr. Romney faces is that whatever he says and whatever he may have done, it is Mr. Giuliani’s simple account of events that is the one that sticks in the mind. And the caucus and primary voters that both men must convince are those not the soft hearted Massachusetts progressives who came to the aid of Mr. Dukakis, they are hard nosed Republican and independent voters who, when thinking about law and order, start from the premise that killers, once caught, should be permanently incarcerated so they are not free to kill again.

If Mr. Romney can free himself from his pressing ethical dilemma as easily as Horton and Tavares escaped prison, he is a far more effective political scrapper than his Hollywood good looks and white collar wealth would suggest.

Mr. Wapshott’s “Ronald Reagan and Margaret Thatcher: A Political Marriage” has just been published by Sentinel. He can be reached at nwapshott@nysun.com.