WASHINGTON — He is a Democrat in a marquee Senate race, pressed by a strong Republican in a state with a challenging political environment. So when a new proposal to limit power plant emissions was seen as posing a threat to allies of the Obama administration, Senator Mark Udall of Colorado acted quickly: He embraced the plan.

“Coloradans have seen firsthand the harmful effects of climate change, including severe drought, record wildfires and reduced snowpack,” Mr. Udall said in a statement shortly after the Environmental Protection Agency plan was made public last week. “The E.P.A.’s draft rule is a good start, and I will fight to ensure it complements the work we have already done in Colorado and provides states the flexibility they need to make it successful.”

The E.P.A. proposal to reduce carbon pollution from power plants was deemed a political gift from the Obama administration to Republicans running for Senate seats in the coal-producing states of Kentucky and West Virginia, and an anchor around the necks of their Democratic opponents. Elsewhere, the threat of higher electricity bills and Republican attacks about another federal power grab were supposed to send Democrats scurrying for cover and distance from the White House.

But Mr. Udall’s example shows that not all Democrats look at it that way.

In Iowa, Representative Bruce Braley, the Democratic Senate nominee, has adopted the same approach as Mr. Udall. “Reducing our carbon output is not only necessary for the health of the planet, it’s an opportunity to continue to improve the health of the Iowa economy — which is and will remain my No. 1 priority,” Mr. Braley said.