Akin circulates video of McCaskill saying emissions reduction due to economy is 'good news'

That did not stop Akin from trying to make hay of the comments, however. The long-term Missouri congressman has been in hot water since remarks he made this summer about "legitimate" rape victims spread nationally, but polls show him remaining competitive in a race against McCaskill he had previously been expected to win easily.

McCaskill voted in 2009 for a procedural motion to advance legislation that would cap U.S. greenhouse gas emissions and create an emissions-credits trading system to help polluters meet their obligations.

The “cap-and-trade” measure stalled amid opposition from most Republicans and some Democrats.

Despite backing the failed attempt to advance the bill, McCaskill wrote to Senate Majority Leader Harry ReidHarry Mason ReidAmendments fuel resentments within Senate GOP Donald Trump is delivering on his promises and voters are noticing Danny Tarkanian wins Nevada GOP congressional primary MORE (D-Nev.) saying she had concerns with the emissions cap proposal.

McCaskill has since said that she would have opposed the cap-and-trade effort if it had come up for a final vote in the Senate, but Akin's campaign said Tuesday that she is "so committed to a cap and trade energy tax that she celebrates a reduction in emissions caused by millions of Americans losing their jobs."

McCaskill has co-sponsored a bill in the Senate this year that would block European countries from applying a similar emissions cap to U.S. airlines for flights that operate in the European Union.

Akin's campaign used the video Tuesday to accuse McCaskill of "putting her liberal agenda ahead of the poor economic situation facing millions of Americans."

McCaskill's campaign did not respond to a request for a comment on the video or Akin's campaign attacks on it.

—Ben Geman contributed to this report.