President Obama heads to Los Angeles on Monday to lend his star power on the stump to Sen. Barbara Boxer, a visit that serves as a reminder that the veteran California Democrat is facing one of the toughest campaigns of her career. 

The president will campaign for Boxer at two back-to-back fundraisers Monday evening. Though the president's personal approval numbers are sagging, he is still a political force in California and his presence a potential boost for Boxer's campaign as she fights for a fourth term. 

The latest Rasmussen Reports poll on the race showed 36 percent of voters view Boxer unfavorably. She was polling ahead of her top Republican challengers by just a few points, earning no more than 43 percent of the vote when matched against any of them. Former Rep. Tom Campbell came closest, with 41 percent. Boxer's two other challengers are former Hewlett-Packard CEO Carly Fiorina and State Assemblyman Chuck DeVore. 

The Republican primary election is June 8. 

At the California Democrats' annual convention in Los Angeles on Saturday, Boxer urged a crowd of party faithful to support her and keep their hopes up. She urged Democrats to start matching the enthusiasm that conservatives are showing for their candidates on the other side of the aisle, telling the crowd to get "as excited as the Tea Party people are." 

She warned that a vote for a Republican candidate for Senate in November would be a vote to "go back to the policies that got us into this mess. We want to forget those eight years that the last administration left us." 

But she acknowledged that "nobody can take their seat for granted." 

"These are tough times we're going through in America and California," Boxer said. "I'm not going to sugar-coat that." 

Californians face a double-digit unemployment rate, making many once-untouchable incumbents like Boxer vulnerable this November. 

Obama is expected to pack the house Monday night and help add to the $9 million already in the Boxer campaign war chest. 

Couples are being asked to cough up $35,000 apiece to hear the president talk Monday night and enjoy a performance by soul singer India Arie. 

A Democratic Party source said the dinner and reception are expected to raise about $3.5 million.