There are other factors that have helped Sanders in Iowa. Because his backers are so loyal, opponents have been unable to penetrate his base, if they have tried to at all. Part of the reason is that Sanders’ strategy revolves around engaging people who typically don’t participate in the political process, a highly difficult group to target; even the Sanders campaign acknowledges it is a risky strategy. Another factor is sheer resignation: His rivals just don’t see the point in trying to pick off supporters who probably won’t budge.