Greenwire: Advocates for Senate climate legislation are pushing back against calls to abandon a mandatory cap on U.S. greenhouse gas emissions in favor of a stand-alone energy bill that some say has a better chance of passing in an election year. For starters, President Obama’s top energy adviser insisted yesterday that the administration’s goal remains a “comprehensive bill” that touches on all corners of the energy and climate debate, including the controversial cap-and-trade program that most …