2. Susan Collins

Not only is Sen. Collins (R-Maine) one of the key swing senators Graham, Kerry and Lieberman will be looking to court, but Collins is the author of competing climate change legislation. Collins and Sen. Maria Cantwell (D-Wash.) in December introduced the Carbon Limits and Energy for American Renewal (CLEAR) Act, which aims to reduce greenhouse gas emissions by forcing companies to bid on carbon permits and directing that revenue back to consumers. Graham, Kerry and Liberman have vowed to roll elements of the CLEAR act into their bill, but if Collins isn’t satisfied with their wording, they could lose her support and potentially destroy the bill’s success in the Senate.

Next: 1. Lindsey Graham