The Keystone XL Pipeline would bring oil from Canadian tar sands to North Dakota. There, it would connect to an existing pipeline that runs to the Gulf Coast of Louisiana. Because it would cross an international border, the State Department must file a statement on the environmental impact. That report came down last week, and while it downplays the impact on global warming, it's just uncertain enough to add fuel to both sides. Republicans see a green light for energy independence. Environmentalists warn of climate disaster. Democrats are divided, with the President caught in the middle -- and control of the Senate might be at stake. Where would the pipeline go? Who would be affected along the route? How has it come to symbolize the conflict between global warming and the economy?