LOS ANGELES (Reuters) - Democratic Senator Barbara Boxer’s edge over Republican challenger Carly Fiorina has dwindled to 3 points as she seeks re-election in November, with more Californians now holding an unfavorable view of the three-term senator, a poll released on Thursday showed.

Boxer, who once held a 30-point lead over Fiorina, the former CEO of Hewlett Packard and a political novice, is now ahead by a margin of only 47 percent to 44 percent, the Field Poll found.

One of President Barack Obama’s staunchest allies who has become a powerful liberal voice in the Senate since she was first elected in 1992, Boxer is facing her toughest challenge yet, as a wave of anti-incumbent sentiment sweeps the nation.

California, normally a reliably Democratic state suffering from double-digit unemployment and a budget deficit running into tens of billions of dollars, is considered a potential bellwether in the coming congressional elections.

The Field Poll found that since January more Californians have become disgruntled with Boxer, with 52 percent of likely voters holding an unfavorable view of her, compared with just 41 percent who regard her favorably.

Boxer’s ratings have dropped to some of the lowest levels of her 18-year career in the Senate, with only 42 percent of registered voters approving of her job performance and 43 percent disapproving.

The survey found that 34 percent of likely voters in California had a favorable impression of Fiorina, compared with 29 percent who viewed her unfavorably.

Fiorina is the overwhelming favorite of voters who identify with the conservative Tea Party movement, while Boxer has a strong lead among those who do not.

Fiorina has focused on job losses and the weak economy during the campaign as she stresses her political outsider status and private-sector roots.