To attract bipartisan support, a proposed federal requirement that utilities use carbon-free energy may need to be packaged with a clause to pre-empt U.S. EPA greenhouse gas rules, key senators said today. Senate Energy and Natural Resources Chairman Jeff Bingaman (D-N.M.) said he would be open to amending his "Clean Energy Standard Act" to include some EPA pre-emption, and ranking member Lisa Murkowski (R-Alaska) said the change would cause her to rethink her current opposition to the proposal.