It doesn't mean the voters would be swoon and persuaded to vote for 0bama. In 2002, Linda Lingle (R) was virtually tie with Mazie Hirono (D) in the race for Hawaii governorship. Hirono brought in a big gun: Bill Clinton. His speech was well received by local media. In couple days, polls showed Lingle started to pull away from Hirono. After the election, which gave Hawaii the first Republican Governor in 40 years, Hirono's camp revealed that their internal numbers also showed movement against her after Clinton's speech.
Interestingly, Lingle and Hirono will face off each other again this year in the US Senate race.