Why would any American candidate do an ad in Spanish

http://thinkprogress.org/2008/01/08/giuliani-spanish/

Rudy ‘Speak English’ Giuliani Releases Campaign Ad In Spanish

Like many of the other GOP presidential candidates, former New York City mayor Rudy Giuliani had tried to portray himself as tough on undocumented immigration. One of his favorite applause lines has been to stress English-only policies: "

Why would he do this? one must speak English to be a citizen
and to vote