In selectorate theory, the subset of those who choose a leader whose support is essential for the leader to keep power; its size relative to the selectorate shapes whether leaders provide public or private goods.
In more detail
In a democracy the winning coalition is a large share of voters; in a military junta or personalist regime it may be a few dozen officers and officials. Bueno de Mesquita and colleagues argue that small coalitions favour private rewards, corruption and long tenure for poorly performing leaders, while large coalitions favour public goods. The ratio of coalition to selectorate defines a loyalty norm: when coalition members are easily replaced, they stay loyal. Measures of coalition size are contested.