Jimmy P has three reasons why cap-and-trade might be doomed to fail. Here's reason number two:
Most people won’t see an immediate benefit. Proposed changes in the U.S. healthcare system wouldn’t immediately change the current insurance coverage of most Americans, despite new government spending and higher taxes. Likewise, cutting carbon emissions will likely incur big costs today with any tangible benefits coming later this century. During a recession, neither provides the sort of cost-benefit analysis that strapped Americans are likely to find compelling.
I would add, more than just that voters don't see the benefits, they probably see the costs. There is strong evidence that when their pockets are being squeezed, consumers look to cut environmentally-friendly spending. Being green, in that sense, is another form of luxury spending—you won't buy the gold plating when you need to cut costs, and you're likely to not buy (or at least, less frequently buy) the luxury of feeling like you're helping the earth as well.
What does consumer spending have to do with cap and trade? The economic times mean that it is especially hard to ask consumers to pay a little bit more in their energy bills. Cap and trade might have to wait until the economy rebounds, when voters are less likely to bristle at having to pay more for the sake of the environment.
An economic recovery would also deal with the third impasse mentioned by Jim—that problems like unemployment are more pressing in voters' minds.