Ezra Klein, to whom 
tcnorris has provided a link for a long time, has written
 an excellent summary of why a bad economy has plagued Barack Obama in the form of a disparaging book review about Ron Suskind's Confidence Men.
Suskind did not get the story right at all, but this summary by Klein does:
It is easy to tell the story of what the White House 
did wrong in its response to the financial crisis: it underestimated it.
 It had good reason to underestimate it, of course. Almost everyone was 
underestimating it. In the fourth quarter of 2008, when Obama’s economic
 team was meeting in Chicago to map out their policies, the Bureau of 
Economic Accounts thought the economy was contracting at a rate of 3.8 
percent per year. It wouldn’t be until this year that we learned the 
economy was really contracting at a rate of 9 percent. And it wasn’t 
just the BEA. The Federal Reserve has been 
continuously overoptimistic. So have the leading private forecasting 
firms, like Macroeconomic Advisers and Moody’s Analytics. And so have 
Wall Street banks like Goldman Sachs and JPMorgan.
The observers who got it right were the ones who could tell a story that didn’t rely 
on the early data. Kenneth Rogoff and Carmen Reinhart, who would publish
 This Time Is Different: Eight Centuries of Financial Folly, 
their epic history of financial crises, in late 2009, saw that the 
recovery would be slow and tough. Economists like Paul Krugman and 
Joseph Stiglitz, who were more knowledgeable about the struggles over 
recession in Japan and had their own Keynesian understanding of 
financial panics, were also suitably pessimistic. 
But early mistakes can be corrected. If the initial stimulus is too small, you 
make it bigger. If your housing policies are too modest, you toughen 
them up. If the private sector sheds jobs and long-term unemployment 
becomes a problem, you begin hiring workers directly.
Or so goes 
the theory. The reality is more troubling. The initial stimulus was too 
small, but there’s no plausible case that Congress would have been 
willing to make it much bigger just because the Obama administration had
 a theory that the financial crisis would lead to a worse recession than
 most forecasters expected. The trouble was that attacking a financial 
crisis with a too-small stimulus was a bit like attacking pneumonia with
 too-few antibiotics: you feel better for awhile, and then it comes 
back. And this time, it’s harder to kill.
The problem is 
political. Having very publicly passed a very big policy that you 
promised would revive the economy, the country blames you when the 
economy does not, in fact, revive. Your policies are discredited and 
your opponents are emboldened. You lose seats in the next election and 
your leverage over lawmakers. So you can’t, with any prospect of 
success, go back to the well and ask for a bigger stimulus or more money
 to buy up bad mortgages. And then, when the economy gets worse, you’re 
simultaneously in charge and out of options. You came to Washington 
promising change and now you’re begging for patience. It’s a crummy 
situation, and there’s no combination of policy proposals or speeches 
that can get you out of it. But this is the vise that has tightened 
around Barack Obama’s presidency.
It seems to me that even those who got it right such as Krugman probably underestimated how much stimulus was actually needed (although 
he foresaw the political consequences). The Obama stimulus was $700 billion and 
Krugman and others spoke of 1.3 billion over two years.  As Klein notes revisions to the data made 
only this year tell us the downturn was much worse than suspected at the time.
We still need lots of stimulus, but the blame for not doing anything now squarely and unequivocally belongs with 
the Republicans and the austerity class, something that 
the media in particular, has had trouble figuring out.
More needs to be done by government in the form of public spending in the U.S., Europe and Canada. The 
mania for deficit cutting and balanced budgets is insane. 
It cannot be said often enough or loudly enough: we must not worry about deficits while the problem is deflation and unemployment.