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 ObamaAs Buttigieg rises, Biden is still the target Debate gives Democrats a chance to focus on unaddressed issues of concern to black voters Is Joe Biden finished? 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.