Washington - When Republicans take control of both houses of Congress next month, President Barack Obama will be hard-pressed to cut US greenhouse gas emissions dramatically - a promise he made to Americans and the world and a key to his legacy.
The Obama administration ballyhooed an agreement with China last month that commits Beijing for the first time to action that would eventually slow its emissions of heat-trapping carbon emissions. That deal reaffirms ambitious US goals under Obama's leadership, but he still may face attempts in Congress to block the money needed to fund government enforcement of emissions rules.
The US-China agreement has provided some optimism for a gathering in Lima, Peru, where representatives of 190 nations are holding talks on a new worldwide deal to limit greenhouse gas emissions and keep global warming from causing irreversible damage.
But in the US, relations between the White House and congressional Republicans are particularly bad these days, and it's not just because of Obama's aggressive actions on climate change. Shortly after the November election gave Republicans majorities in both legislative chambers, the president used his executive power to order big changes in US enforcement of immigration laws.
Obama has temporarily shielded from deportation millions of people in the country without permission, an action that has deeply angered Republican members of both houses, especially the big block of small-government, anti-immigration tea party members in the Republican caucus.
Obama's moves on climate change cut just as deeply, and Republican ire is equally long-standing on that issue. John Boehner, speaker of the House of Representatives, said the president had "poisoned the well," making bipartisan co-operation between the White House and Congress unlikely.
A key Republican senator, who will become chair of the Senate Environment and Public Works Committee, has called climate change a "hoax" and has vowed to block Obama's moves on every front.
"As we enter a new Congress, I will do everything in my power to rein in and shed light on the [Environmental Protection Agency's] unchecked regulations," said Senator Jim Inhofe of the oil-producing state of Oklahoma.
Inhofe's threat was in response to the landmark agreement that commits the US and China, the No 1 and No 2 greenhouse gas emitters, to dramatic action on carbon emissions in the coming years. Inhofe called the agreement "hollow and not believable."
Obama already has moved to cut US emissions through tougher fuel economy standards for cars and trucks and set a "target of reducing its US emissions by 26% to 28% below its 2005 level in 2025."
China, which had previously refused commitments on any emissions reductions, said it intends to have carbon emissions peak around 2030 and to increase the share of non-fossil fuels in primary energy consumption to about 20% by the same year.
Obama's order to retrofit existing coal-fired generating facilities and restrictions on building new coal-fired plants have raised hackles of politicians from big coal-producing states like Kentucky. That state is home to the incoming Senate Majority Leader Mitch McConnell.
He will be able to direct the flow of legislation aimed at blocking the EPA's attempts to enforce the new regulations.
McConnell has said his top priority will be "to try to do whatever I can to get the EPA reined in."
Some Republicans have indicated that they may try to make the passage of overall government funding dependent on congressional agreement to cuts for EPA enforcement.
If that kind of government-funding legislation fails in Congress or if Obama were to veto it, there could be yet another government shut-down for lack of money to keep agencies in operation.
McConnell has vowed to avoid that tactic under his leadership after a Republican-driven shut-down last year that, at the time, damaged the Republican brand.
With Republicans putting together a strategy for the 2016 presidential election, there's a question of how tough they will be in their opposition to measures to fight climate change and other EPA actions to stop environmental degradation.
Polls show that an increasing number of Americans, while still not overwhelmingly concerned about rising temperatures, do think the government should do more to prevent further climate change, even if that has negative economic consequences.