The California race between Democratic incumbent Barbara Boxer and Republican challenger Carly Fiorina remains one of the tightest Senate battles in the country, according to the newest Field Poll out today.

Forty-seven percent of respondents said they'd cast their vote for Boxer, compared with 41 percent who picked Fiorina. The poll surveyed 599 likely voters in the Golden State Sept. 14 through Sept. 21 and has a margin of error of +/- 4.1 points.

The last Field Poll in the race, conducted June 22 to July 5 of 1,005 likely voters showed Boxer leading Fiorina 47 percent to 44 percent. The margin of error was +/- 3.2 points.

The current survey shows that Boxer and Fiorina are winning their bases and picking off the other party's support at an even ratio. Seventy-six percent of Democrats surveyed said they would support Boxer, and 79 percent of Republicans said they would back Fiorina. Ten percent of Republicans said they would cross over and cast their vote for the incumbent, versus 11 percent of Democrats who said they'd pick the challenger.

One statistic in the Field Poll is inconsistent with other polling on the race in recent weeks - the support of unaffiliated voters. Forty-six percent said they would back Boxer versus 40 percent who said they'd back Fiorina. Yet in a Public Policy Polling (D) survey conducted Sept. 14 through Sept. 16 of 630 likely voters, Fiorina won independent voters 50 percent to 38 percent. The margin of error was +/- 3.9 points. PPP noted in its analysis, "What has changed is that Boxer now trails among independents, 38-50, after winning them 48-38 last time."

Regarding Fiorina's positioning in the Field Poll, Republican strategists working with Fiorina point out that the poll was conducted prior to her general election TV ad campaign, which began on Thursday. Boxer had already begun to advertise and is more universally known in the state, but Democrats stress that Boxer has maintained a lead and a level of support that hasn't slipped.

Boxer's favorability rating was 45 percent in the poll, with 48 percent of respondents finding her unfavorable and seven percent offering no opinion. Fiorina also had a higher net unfavorable rating, but she has more room for growth. Her split was 35/38 favorable/unfavorable, but 28 percent said they had no opinion.

The RealClearPolitics polling average shows Boxer in better shape than some of her fellow endangered incumbent Democratic senators: She leads Fiorina in the average by 5.6 points.

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