Obama was to appear at two fundraisers Tuesday night in San Francisco with the liberal Boxer, who is seeking her fourth-term. Though she easily won her last election, the economic woes that have hit California particularly hard have left Boxer facing her strongest challenge since she joined Congress.
Complicating matters for Boxer is an anti-Washington electorate that's been dismissing long-serving politicians with ease in this midterm election year. Veteran Pennsylvania Sen. Arlen Specter, who switched from the Republican to Democratic Party, was ousted in his primary contest last week. Utah's three-term Sen. Bob Bennett failed to make it out of his state's Republican nominating convention earlier this month.
During a trip to Los Angeles last month to headline three fundraisers for Boxer, Obama warned supporters that she could suffer the same fate.
"I don't want anyone here taking this for granted," he said at an April 19th event.
Boxer's opponent will be decided in a June 8 GOP primary that pits former Hewlett-Packard chief executive Carly Fiorina against former Rep. Tom Campbell and California Assemblyman Chuck DeVore, who has the backing of the tea party movement.
Proceeds from Tuesday's events will be split between Boxer's campaign and the Democratic Senatorial Campaign Committee.
Obama will spend Tuesday night in San Francisco, then head to nearby Fremont, Calif., on Wednesday to tour a solar facility and make remarks on the economy.