Nearly one-third of the U.S. population today was born after Ronald Reagan left the White House. They'll never have any personal memory of Reagan, and millions more remember him just as the old guy who was president when they were little. Someone else - teachers, historians, the media - will likely shape whatever opinions they have of Reagan. It's no wonder that a battle is under way for the 40th president's legacy. After recent events commemorating Reagan's 100th birthday in his home of Southern California, it's clear that the guardians of Reagan's legacy - the veterans of his administration, the …