The two are only partially connected, but for a long time have been treated as one as presidential campaigns became their own organization that would give instruction to the DNC/RNC. I would argue that having a viable candidate should actually be the last element, not the first.
The recent tradition has been the national committees keep the seats warm and build out the national organization, then hand over the keys (and leadership roles) to the presidential campaigns. A fast convention will mean that in most states, there isnât much of an organization - characteristically, the state nomination campaign morphs into the state presidential campaign committee with some resources parachuted in from the national level. But those state nomination campaigns wonât be significant for many states that selected delegates after the nomination was over.