Former New York City mayor Rudy Giuliani (R) says he knows that lower taxes yield more revenue.

In his latest TV ad, Giuliani says Democratic presidential hopefuls Sen. Hillary Rodham Clinton (N.Y.), Sen. Barack ObamaBarack ObamaJean-Claude Juncker is Europe's shirker-in-chief Trump to governors: Healthcare plan will be 'very special' DHS may relax hiring requirements to meet border agent goal: report MORE (Ill.), and former Sen. John Edwards (N.C.), "are making the promise to raise taxes."

"The only thing I can tell you in addition to that is they'll raise taxes even more then they promise," Giuliani says.