President Obama called this weekend for the Senate to get to work in passing comprehensive energy and global warming legislation now that they have a blueprint in Friday's House-passed measure. Using his weekly radio and Internet address as a bully pulpit, Obama emphasized the economic incentives and national security implications that he said would come if he were to sign into law a new U.S. energy and climate policy. But the four-and-a-half-minute speech also highlighted the difficult political challenges ahead, especially with more than a dozen Democrats and nearly all Republicans in the Senate still pushing back against such sweeping changes.