By 51-40%, the American people don't think the president's "jobs plan" will bring down unemployment.

That's the result found in a Bloomberg poll that also showed significant erosion of the president's core support from 2008:

A majority of Americans don't believe President Barack Obama's $447 billion jobs plan will help lower the unemployment rate, skepticism he must overcome as he presses Congress for action and positions himself for re- election.

The downbeat assessment of the American Jobs Act reflects a growing and broad sense of dissatisfaction with the president. Americans disapprove of his handling of the economy by 62 percent to 33 percent, a Bloomberg National Poll conducted Sept. 9-12 shows. The disapproval number represents a nine point increase from six months ago.

The president's job approval rating also stands at the lowest of his presidency -- 45 percent. That rating is driven down in part by a majority of independents, 53 percent, who disapprove of his performance.

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Of the respondents who said they've supported Obama at one point since he launched his presidential campaign in 2007, fewer than half say they still support him as fervently. Thirty- seven percent say their support has waned and 19 percent say he lost their backing because they've grown disappointed or angry with his leadership.

Almost a third of Democrats and Democratic-leaning respondents say they'd like to see Obama face a primary challenge.

The job performance areas where Obama scores favorably are his handling of the situation in Libya and fighting terrorism. Another rare bright spot in the poll is his favorability rating, which stands at 50 percent and is better than all of his prospective Republican rivals. House Speaker John Boehner, an Ohio Republican, has a favorability rating of 33 percent compared to 38 percent who view him unfavorably, a ten point jump from June before the debt ceiling standoff in August.

There's a downside to his favorability rating as well; 47% do not have a favorable opinion of the president. That is an extremely high unfavorability number and it shows just how polarizing this president has become.