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 Hussein ObamaGeorge W. Bush honors father at benefit for hurricane victims Dem senator: ‘I miss every one of’ our last 5 presidents All five living former presidents appear at hurricane relief benefit concert 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.