Remember when Republicans hoped that Barack Obama’s declining job approvals would help the GOP limit him to the coastal states?  According to the latest Field Poll in California and the results of the NY-09 special election, Democrats may have to hope that Obama can actually carry the coastal states:

Even in heavily Democratic California, President Barack Obama’s job approval rating has plummeted among voters, largely on his handling of the economy, according to a new Field Poll.

Though Obama is strongly favored to win California in his re-election bid next year, the poll suggests many Democrats may vote for him only begrudgingly, and it is yet another indication of weakening support nationwide.

“When you’re seeing vulnerability in a state like California, I think that really is ominous for his national standing,” Field Poll director Mark DiCamillo said.

For the first time since Obama took office in 2009, less than half of California voters – 46 percent – approve of the job he is doing, just two percentage points more than disapprove, according to the poll.

“Plummeted” is correct.  In June, his approval rating was a comfortable 54/37, with a gap of 17 points.  Obama has lost 15 in the gap in just three months.  The lowest gap in the Field series before this month was 12 points, which came last September, a few weeks before his party got buried in the Tea Party midterm avalanche.

Obama has lost ground in all subgroups in the poll, save one.  Obama gained a point among those identifying strongly with the Tea Party, going from 3% in June to 4% in this poll.  Otherwise, Obama took hits in all areas.  He did worst among Asian voters (-16 to 48/34), independents (-13, 45/43), not surprisingly in the Central Valley (-13, 35/56).  The Central Valley had much of its irrigation water cut off because the federal government intervened on behalf of the Delta smelt and turned one of the nation’s richest agricultural areas into a near-desert.

There are other warning signs in this poll, too.  His standing among Democrats dropped by 10 points, most likely on Obama’s activist-base Left.  He now polls significantly under water with men, 42/48, having been up 52/38 in June.  Obama still performs solidly among voters under 40, but now trails with all age demographics 40 and older.  Three months ago he commanded majorities in all age demographics.

Does this show that Obama could lose California in 2012?  It’s still unlikely.  Democrats control the state legislature and executive, and Obama scores majorities in the two major population centers of Los Angeles and San Francisco — although lower majorities at the beginning of the summer.  However, Democrats and the Obama campaign can no longer take the state for granted, using it only as an ATM to fund campaigns in other states.  They will have to spend money, probably a lot of it, to keep California blue in 2012.  That means that the state won’t be much of a net profit center for Obama 2012, and that will have a big impact in other areas of the country.  If they have the same problem in New York, and the NY-09 results appear to indicate that, the middle of the country should open wide for the GOP nominee, and Republicans could be poised to score big gains in the Senate and House races in 2012 as well.