An "ominous" new poll shows Sen. Barbara BoxerBarbara Levy BoxerFirst senator formally endorses Bass in LA mayoral bid Bass receives endorsement from EMILY's List Bass gets mayoral endorsement from former California senator MORE’s (D-Calif.) approval rating tanking as Vice President Joe BidenJoe BidenOvernight Energy & Environment — Presented by American Clean Power — Methane fee faces negotiations White House rejects latest Trump claim of executive privilege The No Surprises Act:  a bill long overdue MORE visits the state to help her raise money.

Biden will be in Silicon Valley and Los Angeles on Thursday to help Boxer gather contributions for her reelection run against Republican Carly Fiorina.

A new Field Poll gives Boxer some of the lowest approval ratings of her three terms in office. The poll also found  the race between Boxer and Fiorina is a statistical toss-up.

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"She is vulnerable," Field Poll director Mark DiCamillo told the San Francisco Chronicle. "This is very ominous for her."

In the June 22-July 5 survey, Boxer led Fiorina among registered voters by the slim margin of 47 to 44 percent. Boxer was viewed unfavorably by 52 percent of respondents, while 43 percent disapproved of her performance and 42 percent approved.

Among the "likely" registered voters surveyed, 48 percent disapproved of Boxer's performance and 42 percent approved.

Fiorina's campaign trumpeted the results.

"Today's Field Poll results prove that California voters are ready to fire Barbara Boxer," Fiorina spokeswoman Julie Soderlund said in a statement.

The Field Poll of 1,390 people had a margin of error of 3.2 points.