With legislation hung up in the Senate, developed and developing countries alike might be skeptical of the United States' commitment to addressing climate change problems.
Here are some of the questions facing U.S. negotiators as they approach Copenhagen and attempt to allay those concerns:
* CAN THE U.S. PUT ON A BRAVE FACE?
The world's second biggest polluter of carbon dioxide will be in the difficult position of trying to cajole China, India and other major polluters to promise to cut their emissions. Nevertheless, the United States will likely try to downplay its own shortcomings and accentuate the positive.
After eight years of relatively few accomplishments on the climate front during the Bush administration, President Barack Obama's negotiators can argue there's been a major shift.
In less than a year, the U.S. House of Representatives passed a climate bill; a similar one is pending in the Senate and the Environmental Protection Agency is requiring domestic automakers to significantly reduce tailpipe carbon emissions.
Furthermore, the EPA has taken steps toward regulating smokestack emissions of carbon for the first time.
* WHAT ELSE CAN THE U.S. PROMISE?
Even if Congress can't pass legislation next year, U.S. negotiators can tell Copenhagen the EPA is waiting in the wings. By March or so, the agency could produce initial regulations for limiting carbon emissions.
The regulatory route is not Obama's desired path; he wants more comprehensive legislation. But the EPA has made clear it would proceed without Congress if need be.
Negotiators also could stress that there's still hope for Congress to pass a comprehensive bill. If "cap and trade" won't work for U.S. lawmakers, they might try an alternative.
They also could point out that the United States has a long history of approving major environmental laws in an election year, which 2010 is.
* CAN THE U.S. BUY ITS WAY OUT OF TROUBLE?
Experts think Washington could go a long way toward building confidence for a global deal if the United States put forth a specific proposal on how much money it would throw into an international pot.
The funds would be dedicated to helping poor countries develop alternative energies and deal with the fallout from global warming. Tens of billions of dollars could be required annually.
A problem: In tough economic times and with astounding domestic budget deficits, many members of the U.S. Congress would be nervous about promising money for others.
* IS THERE A FALLBACK OPTION?
The head of the European Commission, Jose Manuel Barroso, said on Tuesday a full-fledged climate deal would not be reached at Copenhagen but it was still possible to develop a framework agreement.
Many U.S. environmental group agree, and are already asking their government's negotiators to push for a substantive interim deal.
Last July, major economic powers, including the United States, agreed to work toward limiting global warming to 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial levels, and this could provide a useful backdrop to an interim deal.
Experts say the best that can realistically be hoped for from the meeting is an agreement that has the 190 nations accepting the 2 degree goal, a new specific date for wrapping up a final deal and progress on how a new global carbon-reduction scheme would be enforced.
* WHAT IS THE WORST CASE SCENARIO?
The Pew Center on Climate Change sees the worst case scenario coming out of Copenhagen as one in which countries blame any summit failure entirely on the United States.
If the talks fall into disarray, a "blame the U.S." plot line would likely deepen opposition in the U.S. Congress to comprehensive climate control legislation and deliver an additional setback to international talks -- one that some fear could take a decade or so to recover from.
Todd Stern, the lead U.S. negotiator, would have to employ all his diplomatic skills if he sees the world ganging up on Washington.