The pressing energy issue in the 2008 presidential campaign was how to reduce carbon emissions and limit global warming. Four years later, the drive for "green energy" has been replaced by a new imperative: the need to end U.S. dependence on foreign oil.
"I will set a national goal of North American energy independence by 2020," Mitt Romney declared during a campaign speech in August. "That means we produce all the energy we use in North America."
He reiterated that goal in the opening minutes of the presidential candidates' debate in Denver this week.