Romney’s financial contributors also have green baggage, including Connaughton and Mistri.

Connaughton was one of the few Republicans willing to speak out publicly during the first two years of the Obama administration in support of carbon caps, even offering ideas for how the White House could get a bill through the narrowly divided Congress. His remarks were made as an executive vice president for Baltimore-based Constellation Energy, a power company with a large nuclear portfolio that would stand to benefit from carbon limits.

Jeff Holmstead, a former Bush-era EPA official who supports Romney, said he didn’t think the former Massachusetts governor should be that concerned about leaning on people who in the past have advocated for climate policies.

“Anyone who’s been active at all in the public policy world has probably talked about the desirability of a carbon tax or how you might structure cap and trade,” said Holmstead, now an industry attorney at Bracewell & Giuliani. “I just think it’s a stretch to connect their past interest or even support to those things with Romney.”