A new poll from California shows Dianne Feinstein falling below 50% in re-elect support, a rating than in any other state might mean something.  McClatchy sends up the red flag from the latest Harris Poll, which gives the four-term Senator only a +4 on support for a fifth term, hitting below 50%:

Democratic Sen. Dianne Feinstein remains more popular among California voters than her colleague Barbara Boxer, a new Field Poll shows.

But Feinstein can’t rest easy as she prepares for another re-election bid next year. For the first time since her initial 1992 election, less than half of the Californians surveyed consider themselves leaning toward Feinstein.

“It’s somewhat surprising, because she’s considered by many to be among the most popular politicians in California,” Field Poll director Mark DiCamillo said Wednesday.

Forty-six percent of Californians surveyed between Feb. 28 and March 14 said they are “inclined” to vote for Feinstein next year. Forty-two percent are “not inclined,” and 12 percent call themselves undecided.

My friend Eric Ostermeier at Smart Politics takes a hard look at the data, and says Feinstein should be worried:

For starters, the senior Senator from California’s job approval rating has been languishing in the 40s for well over a year and has been on the decline for half a decade.

SurveyUSA’s most recent poll from February of this year found Senator Feinstein with only a 43 percent approval rating – down by more than a quarter from the 59 percent rating she received in November 2006 when she was elected to her fourth term.

That means Feinstein has suffered through a 29-point net drop in job approval from her reelection in November 2006 (+25 points; 59 percent approve, 34 percent disapprove) to February 2011 (-4 points; 43 percent approve, 47 percent disapprove).

And the February poll is not an aberration.

On job approval, Feinstein is actually under water at 43/47.5 in Survey USA polling this year (averaging two iterations).  That’s about the same as last year’s 43.5/47.8 over 12 polls, when Barbara Boxer withstood a tough election against Carly Fiorina.  Eric does even more number-crunching and discovers that only 23 of the 140 Senators to have won four or more terms in office failed to win 60% of the vote in at least one of those first four elections, and Feinstein has only gotten as high as 59.4% — in her last election, in the Democratic wave of 2006.

National Journal’s Hotline throws a dash of cold water on the Feinstein-is-vulnerable analysis:

46 percent of California voters surveyed said they would be inclined to vote for Feinstein in 2012, while 42 percent said they would not be inclined to do so. During the year before her previous reelection campaigns, Feinstein’s reelect percentage has consistently been over 50 percent in the Field Poll: 53 percent of registered voters were inclined to reelect her in a poll released in March of 2005, while that figure was 59 percent in March of 1999. In a June 1993 poll, the figure was 58 percent.

Still, there are encouraging signs for Feinstein.

48 percent of California voters approve of the job Feinstein is doing, while just 33 percent disapprove, according to the survey. That figure is higher than Sen. Barbara Boxer‘s (D-Calif.) October 2009 44 percent approval rating.

It’s encouraging news for Feinstein; Boxer, despite attracting a well-known and well-financed GOP opponent in Carly Fiorina, still won by ten percent. The 2012 presidential election should also boost Feinstein’s chances in the heavily Democratic state of California.

The sample for the Harris poll was also rather small for a state the size of California, only 444 registered voters.  Harris and Field are considered the leading pollsters in the state, but given the wide geographical distances and disparities in the Golden State’s electorate, that seems too small to be a reliable predictor for an election eighteen months away.

Also, one would have to presume that California would vote for a Republican for statewide office to believe that Feinstein is really vulnerable.  The GOP didn’t win one such office in 2010 despite the Republican sweep across the rest of the nation and the disastrous economy in their own state.  They re-elected Boxer, for Pete’s sake, and stuck a 72-year-old retread in the Governor’s office 28 years after serving his first two terms in that office — by fourteen points.  In 2012, with Barack Obama at the top of the ticket, Feinstein will be one of the few — perhaps the only — Senator who will benefit from his presence.

The GOP will robustly contend for Feinstein’s seat, but don’t expect any miracles.  About the best that could happen would be to force Democrats to spend a lot of money defending her, and keep them from spending it elsewhere.