The Sierra Club plans to highlight differences between candidates on energy issues. The green group touts that in 2014 it will mobilize its 2.1 million members and supporters to continue the momentum it built in 2013 races in Virginia and Colorado, where candidates it backed won reelection.

“Americans widely support climate solutions like accelerating job-creating wind and solar energy growth, tackling dangerous carbon pollution from dirty power plants, securing strong strangers to protect our air and water, and protecting our public lands from destructive drilling and mining — we will help ensure the contrasts between candidates on these issues are clear,” Sierra Club Director Michael Brune wrote in an email to The Hill.

McConnell, the most endangered Senate GOP incumbent, must prevail in a GOP primary and then fight off a highly touted Democratic opponent in Alison Lundergan Grimes, Kentucky’s secretary of State.

McConnell has signaled he believes he can win by tying Lundergan Grimes to Obama and the Environmental Protection Agency.