The parties in the US are pretty damn weak. And their ability and interest in overthrowing their own members is limited. They need to focus resources on the bat

The parties in the US are pretty damn weak. And their ability and interest in overthrowing their own members is limited. They need to focus resources on the battleground states. So in the US, parties are much less less powerful. In Britain, you basically get removed from the party very quickly and as an independent its incredibly hard. Trump is only the latest example of how parties are weak in the US.