"Jerry Brown is still very much the candidate to beat and has run a great campaign to date," said former Clinton adviser Chris Lehane. "But in the world of endorsements, this is certainly one of the real 'gets' that can translate into something. The Clinton name is still golden in the Golden State."
If the Brown campaign portrays the Clinton endorsement as lingering sour grapes over the 1992 campaign, Lehane said he thinks it could backfire.
"Bill Clinton is one of the most popular Democrats in California," Lehane said. "The last thing in the world you would want to do is inject some conflict into this endorsement, because it would just get it out there in a bigger way."
"When you're dealing with one of the most popular people in the party, the more that people hear about him endorsing your opponent, the less good it is," he said.
While California has never in recent memory seen a former president intervene in a competitive statewide primary, Bill Clinton has already done it in two other 2010 races including Rep. Kendrick Meek's, D-Fla., Florida Senate race and Lt. Gov. Lee Fisher's Ohio Senate race.
Given the efforts that Clinton is making on behalf of several of his wife's backers around the country, the Brown camp may try to dismiss Clinton's endorsement as simply the latest obligatory stop on the former president's "payback tour."
Tulchin said, however, that the Clinton endorsement cannot be dismissed so easily.
"Clinton could have easily taken a pass," Tulchin said. "The fact that he is coming out now is a bold move."
The key going forward, according to Tulchin, is just how big of an investment Clinton makes in this race.
"For Gavin to benefit from this fully, he needs significant help raising money," Tulchin said. "If Clinton can help Gavin raise money, then Clinton gives Gavin the resources he needs to sell his story."