The Obama administration had assumed that a plan to cap U.S. greenhouse gases and allow emitters to trade carbon allowances would help funnel millions to developing countries for climate projects such as preserving tropical forests. Now that approach is politically dead. And even the administration's ability to provide direct climate assistance to poor nations over the next two years is in doubt, as a looming budget battle with Republicans could freeze U.S. foreign aid at this year's levels, if not cut it.

"Foreign aid, though, is at the top of the hit list for spending hawks in the new Congress," Michael Levi, a senior fellow on energy and environment at the Council on Foreign Relations, wrote in a blog in mid-November.

Emission pledge in corner

The United States, which never joined the Kyoto pact, has reiterated its emissions cut pledge made last year in Copenhagen. Obama pledged then that the United States, which over history had emitted more greenhouse gases than any other country, would cut the pollution about 17 percent from 2005 levels by 2020.

"The President has made clear and we have made clear that the United States is standing behind the pledge that we made last year ..." Stern told a press briefing on Nov. 22. "There are different ways to skin the cat."

However, negotiators from developing countries asked the Obama administration to provide a more detailed accounting on how it would hit the target.

According to Stern, the U.S. has done "significant things" to control carbon dioxide emission. For example, the U.S. Environmental Protection Agency (EPA) has put in place the "most aggressive" vehicle standards ever.

But the EPA's authority to regulate greenhouse gas emissions, touted by Obama as a key tool to fulfill his promise under the Copenhagen Accord, will be challenged by Republicans in a new Congress.

The GOP has already locked the EPA as a target for some time and will certainly ramp up their fight to restrict the agency's ability to regulate greenhouse gas emissions.

According to analysis by the U.S. media, after midterm elections there appear to be at least 57 votes in the Senate for a measure to delay the EPA's climate rules. That is 10 more votes than a similar measure had in June, when 47 senators supported a proposal by Sen. Lisa Murkowski (R-Alaska) to strip the EPA of the authority to regulate greenhouse gases.

Though Obama could veto such a measure, Republicans are still able to stop EPA regulation by explicitly blocking the EPA's funding to administer such regulations.

In sum, U.S. negotiators would find it difficult to reassure other countries that the U.S. is serious about addressing climate change and moving to a low-carbon future. And of course, the U.S. inaction on climate will definitely weigh heavily on Cancun talks.