From an outsiders perspective I would think that people target interest groups to get campaign funds, then activists to to get campaign workers and last voters

From an outsiders perspective I would think that people target interest groups to get campaign funds, then activists to to get campaign workers and last voters when there is just a short time left that neither money nor worker will improve polling results. But then we have preliminaries and other pre-elections where polling results will influence where both money and people will go, so I would guess the split between the three goes up and down through out the years before general election.