After showing national voters for the first time his caustic personal style of politics, and amid ongoing innuendo about his time in City Hall, Mayor Giuliani is plagued by sliding poll figures in key early states and is being forced to retool his presidential campaign.

An appearance on NBC’s “Meet the Press” on Sunday morning, which a month ago might have seemed routine, has taken on a new importance, coming at a time when confidence in Mr. Giuliani’s ability to win the Republican nomination appears to be melting away. The keynote interview with Tim Russert is seen by the Giuliani campaign as a firewall that must bring to a halt two weeks of troubling news for their candidate, which is reflected in his dipping poll numbers.

Once the undoubted Republican front-runner, the former New York mayor has lost momentum recently thanks to the rapid rise in the fortunes of a former Arkansas governor, Michael Huckabee. But Mr. Giuliani’s personal issues have also worked to smother his appeal as the candidate with a solid record in government most likely to be able to beat Senator Clinton in a general election.

At the Republican YouTube debate on November 28, many Republicans were surprised at the venom with which Mr. Giuliani turned on his rival Mitt Romney, who until recently was the frontrunner in Iowa and New Hampshire, with the renewed accusation that the former Massachusetts governor had employed illegal immigrants to cut his lawn.

And the lingering suggestion that emerged earlier that day — that the cost of Mr. Giuliani’s security detail while he was wooing his third wife, Judith Nathan, in the Hamptons was hidden in the accounts of obscure city agencies, coupled with the impending trial of his former police chief, Bernard Kerik, for fraud — has left some wondering how many more skeletons will emerge from his City Hall years.

Mr. Kerik’s continuing legal troubles are acting as a reminder to voters that Mr. Giuliani’s personal loyalty to lieutenants can prove embarrassing. Mr. Kerik will reappear in court in White Plains on Thursday to answer charges of tax evasion and corruption; his defense lawyer, Kenneth Breen, accused prosecutors in a letter yesterday of “tainting the jury pool and irreparably harming Mr. Kerik’s ability to obtain a fair trial.” Even Mr. Giuliani’s association with his security firm, from which he announced his resignation this week, has proved contentious. “Everything I did at Giuliani Partners was totally legal, totally ethical. There’s nothing for me to explain about. We acted honorably, decently,” he protested on November 5.

As a result of the flurry of bad news stories surrounding him, Mr. Giuliani has been taking a pounding in the polls. According to a national Republican poll average compiled by RealClearPolitics.com, he has fallen to 25% today from nearly 40% in September, with a 5% slide in the last week.

Although Mr. Giuliani has discounted the importance of early states Iowa and New Hampshire, his popularity there, too, is waning. While until the middle of October Mr. Giuliani was in second place to Mr. Romney, since the precipitous rise of Mr. Huckabee he has fallen in the last month to equal third place.

The same is true in New Hampshire. From running neck and neck with Mr. Romney at the end of September, Mr. Giuliani now tails his rival by 16 points. In both Michigan, whose primary is January 15, and Nevada, on January 19, Mr. Giuliani is in a statistical dead heat with Mr. Romney.

Mr. Giuliani’s early lead in South Carolina, which votes January 19, has disappeared, and it is not until the Florida primary on January 29 that he can feel confident of winning a state.

By that time, however, with four states having voted, Mr. Giuliani may have left it too late to establish himself as the irresistible presidential candidate. He may be obliged to rethink his “big state” strategy, which concentrates his efforts on states such as Florida and California, with large legions of Republican delegates to be won. Even one of his most important claims, that he and he alone can beat Mrs. Clinton, has not been true for two months, according to RCP’s poll average. Of the 30 polls since October 1 pitching Mr. Giuliani against Mrs. Clinton, just three have shown the mayor ahead.

This Sunday’s interview with Mr. Giuliani is seen by campaign managers as a way of turning things around. Mr. Russert is expected to press hard on the key personal issues that appear to have led to Mr. Giuliani’s eclipse. These include his idiosyncratic running of City Hall, which led to the appointment of his driver, Mr. Kerik, as his police chief; taxpayers paying for security during his adulterous Hamptons tryst; and the unattractive flash of steel Mr. Giuliani displayed while trying to take the gloss off Mr. Romney’s stance on immigration.

The mayor’s response to such grilling may be the deciding factor in whether his campaign can regain the initiative in an increasingly tight and bitter race.