Why can party factions weaken a prime minister even when the party has a legislative majority?

Party factions can weaken a prime minister even when their party holds a legislative majority because the prime minister’s authority often depends on their ability to maintain party unity and manage internal divisions. When a party is composed of strong, semi-independent factions, the prime minister may be viewed as a compromise figure rather than an uncontested leader, struggling to hold disparate groups together.1

In such environments, the prime minister may lack the influence to dictate policy or control the legislative agenda, as they must constantly balance the interests of these factions to ensure the government's survival. If internal divisions become deep, the prime minister’s power and prestige can decay, leaving them unable to exert firm control over their own cabinet or the civil service. Furthermore, if backbenchers or factional leaders perceive the prime minister's policies as contrary to their interests, they may organize rebellions, forcing the leader to scale back or abandon key legislative goals, which further undermines their standing within the party. Ultimately, a prime minister’s strength is tied to their capacity to command a united front; without it, their leadership becomes precarious regardless of the party's numerical majority.123