The Clinton's relationship with Newsom goes back a long way, back to 2003 when Newsom was running for mayor. Tuesday's endorsement is however unprecedented.
President Clinton's endorsement of Newsom is highly unusual. In fact, it's the first time a former president has ever endorsed a primary candidate running for any state office in California.
"I'm honored to have President Clinton's endorsement," says Newsom.
Newsom says the impact has yet to be determined. It'll depend on how much of presence Bill Clinton will be in the Newsom campaign.
"Its uh we're having those conversations, we're going to be spending a good part of the day together on October 5 in Southern California," says Newsom.
And it's in Southern California where Clinton's backing could be most effective because of Clinton's pull with Latino voters says ABC7 political analyst Professor Bruce Cain, Ph.D.
"In short, it brings money and potentially votes in this primary at a time when Gavin Newsom really needs an injection of both if he's going to be competitive with Jerry Brown," says Cain.
Newsom is trailing badly in the money race, Jerry Brown has twice the war chest and in the polls Brown is also way ahead. A statewide poll taken in August shows Brown with a 29 point lead and in another poll Newsom is trailing by 17 in his own home town.
"I recognize that I don't have the name ID that the former governor does and I have to work harder," says Newsom.
Why Bill Clinton would jump in behind Newsom with Brown so far out in front, speaks to the future in that there is still a lot of time for Newsom to close the gap. Early polls can change and it may also speak to the past.
In 1992 presidential debate, bad blood between Clinton and Brown boiled over. "You should be ashamed of yourself for jumping on my wife. You're not worth being on the same platform as my wife," said Clinton at the time.
If politics is at least in part about relationships, this relationship has had a lot of baggage.
Jerry Brown said on Tuesday, he's not worried about Clinton's endorsement of Newsom.
"Not at all not at all. The people in California are hurting. When they elect the next governor they're going to say, 'What are you going to do about my life? Not who's standing behind you, but are you standing behind us, the people of California?'" says Brown.
Cain says Brown, like Clinton, also has a lot of pull with Latino voters, particularly in Southern California. Right now Brown is the favorite according to the polls, but he is also yet to officially declare his intent to run.