Democratic presidential rivals Hillary Rodham Clinton, Barack Obama and John Edwards campaigned separately in the early voting state of Iowa, urging thousands to make environmental protection a top campaign issue. They marked Earth Day by promoting proposals they said would increase energy conservation and cut down on pollution. "Today is Earth Day, and I personally believe every day should be Earth Day," Clinton said Sunday. "We have a duty to protect God's creation and we have a responsibility to repair the damage that we do as we go on in life."