President Obama lent his voice last night to the push for a mandatory cap on greenhouse gas emissions, using his first speech to a joint session of Congress to lobby for controversial legislation sure to spark a heated debate during tight economic times. Obama campaigned for president last year with climate change and energy issues atop his agenda. And he returned to those themes yesterday, saying that a cap-and-trade bill would help spark economic recovery by giving U.S. companies greater incentive to start producing more wind turbines, solar panels, biofuels and battery-powered automobiles. "To truly transform our economy, to protect...