Use 'loyalist' when somebody supports a regime especially when power dynamics are shifting. Despite the uprising, the loyalists held a rally in the city center.
Pro Tip 2/3
Beyond Politics
'Loyalist' can apply beyond politics, to any institution or leader facing opposition. He was a loyalist of the old school board, refusing to criticize it.
Pro Tip 3/3
Hardship Endurance
A 'loyalist' often implies dedication and support through difficult times or unpopularity. The company's loyalists continued to buy their products amidst scandal.