Rudy Giuliani began to recast his public persona Monday in New Hampshire by pointing voters to his pre-Sept. 11 record, but the former New York City mayor first had to fend off questions about the mounting investigation into former New York Police Commissioner Bernard Kerik.

Kerik, who Giuliani once pushed to lead the U.S. Department of Homeland Security, is under investigation on what could be multiple felony charges. Giuliani said he hadn't spoken lately to his friend and one-time business partner and had no idea what implication a Kerik indictment or plea deal could have on his presidential campaign.

But the Republican presidential candidate stood by Kerik's record in New York while Giuliani was mayor.

"I think Bernie Kerik, I should have checked out more carefully. I've said that. I've apologized for it. But the reality is we brought down crime in record proportions, we brought down violence in the prisons by record proportions," Giuliani said during a campaign stop at a pizza parlor in Manchester, N.H.

"But when you look at the combination of the mistakes and the correct decisions I've made, I think if I made the same balance of those decisions as president of the United States, the country would be in great shape," he continued.

Giuliani has accepted responsibility for his role in Kerik's embarrassing 2004 withdrawal as President Bush's Homeland Security nominee after revelation of tax problems. Ethics questions and corruption allegations also swirled around Kerik at the time.

Federal prosecutors in New York have spent more than a year pursuing criminal charges against him, reportedly including bribery, tax evasion, obstruction of justice, providing false information and conspiracy to eavesdrop. Kerik rejected a plea deal in the spring, but meetings have continued.

Despite the attention on Kerik and the candidate's being dogged on the campaign trail by a man in a Giuliani mask carrying a sign that says "Free Bernie," Giuliani made time Monday to highlight his earlier days as a Department of Justice official under Ronald Reagan, and then as a crime-fighting U.S. attorney and mayor. His campaign is expected to steer focus toward his tough-on-crime history over the next week, with new Web videos and campaign literature.

The shift could help Giuliani overcome critics' characterizations of him as a one-dimensional, anti-terror candidate whose campaign is inextricably tied to his performance as mayor during the Sept. 11, 2001, terror attacks.

"I have a long, long history and a long record way before Sept. 11. I think it's that record, that background — that's the reason I would be a good president," Giuliani said Monday in New Hampshire. "I've had more executive experience than any of the people running."

Giuliani took credit for driving organized crime out of parts of New York City, as well as bringing down unemployment.

"You would have to say that most of my decisions were the correct decisions, even though I've made some wrong ones," he said.

Though Giuliani leads the Republican pack in most national polls, he consistently trails former Massachusetts Gov. Mitt Romney in polls in early-voting Iowa and New Hampshire. Romney and other GOP opponents have also questioned Giuliani's credentials on issues other than terror- and crime-fighting, with questions raised about his positions on immigration and gun control, among others.

FOX News' Carl Cameron and Mosheh Oinounou and The Associated Press contributed to this report.