David Keene , a towering figure in the growth of the modern conservative movement who was equally comfortable in the weeds of grassroots politics and in the corridors of power in Washington , died Sunday after a battle with pancreatic cancer. He was 80. Mr. Keene spent years at the pinnacle, forging the Conservative Political Action Conference into the must-attend event for Republican White House hopefuls and shepherding the National Rifle Association at the peak of its influence. He then