Democratic nominee Hillary Clinton is not ruling out the possibility of a federal appeals court striking down portions of President Obama's landmark climate regulations, a Clinton adviser said.

Trevor Houser said Wednesday that even though the Clean Power Plan has been halted by the Supreme Court until all legal review is competed, Clinton is "optimistic that it will be upheld."

Oral arguments will be heard Sept. 27 in the D.C. Circuit Court of Appeals, just about five weeks before the election in November.

Houser suggested Clinton's campaign has thought through scenarios in which federal judges send the rule back to the Environmental Protection Agency to make fixes, which would mean reproposing the plan under a Clinton presidency.

"They may have technical issues, in which case it gets redesigned, re-proposed," Houser said.

The Clean Power Plan is being challenged by more than two dozen states, dozens of industry groups and others who argue that the plan oversteps the boundaries of EPA's authority and is unconstitutional. The plan requires states, rather than power plants, to reduce greenhouse gas emissions by a third by 2030. Those challenging the climate plan say EPA has authority to regulate emissions only from power plants, and by requiring states to comply is brazen overreach of its powers under the law.

The Democratic National Convention platform supports the Clean Power Plan with other EPA emission rules to curb global warming. "Democrats are committed to defending, implementing and extending smart pollution and efficiency standards, including the Clean Power Plan, fuel economy standards for automobiles and heavy-duty vehicles, building codes and appliance standards," the platform says.

Many scientists blame greenhouse gas emissions from the burning of fossil fuels for causing the Earth's temperature to rise, resulting in potentially catastrophic events such as more widespread drought and flooding.