ANCHORAGE — Watching training sessions at a Regional Elite Group camp, the summer training series held around the country for the nation’s top junior skiers, is one part tantalizing glimpses of the future of American skiing, ten parts the cumulative reality of a lot of focused work in the present. These kids are fast, they are committed, and they are strong. But long-term success in endurance sport takes time, and they know it. Judging from...