GARMISCH-PARTENKIRCHEN, Germany — Perched on a glacier above this storied ski resort, Henry Collarain was having trouble shepherding his three sons toward the ski lodge. “They just love skiing on a sunny day,” he said during a break on a snowy ridge. A contractor from Wisconsin who works at a nearby NATO school, Collarain is one of many Americans you’ll bump into here. But maybe not for much longer, as looming budget battles in Washington may spell the end of US bases in Germany and other rich countries.