It's more complicated than that. In tight races like this you need your party to fall in line, including the larger "extreme" factions. Push too hard away from

It's more complicated than that. In tight races like this you need your party to fall in line, including the larger "extreme" factions. Push too hard away from them and you lose them as voters (e.g. Bernie's supporters in 2016). It's also hard to re-orient a party comprised of thousands of politicians and tens of thousands of operatives in an autonomous media ecosystem moving moving billions of dollars annually to influence public opinion, not to mention an adversarial opposition of roughly the same size and intelligence. There's a narrow space in which an individual campaign can draw battle lines, implement strategies, communicate intent, and maneuver around obstacles. Parties may have a bit more leeway due to coordination but at some point you're trying to herd cats (or otherwise riding a wave over which you have no control).