A principal claim for parliamentary systems, which today make up the majority of democracies, is their responsiveness and flexibility. Parliamentary governments, especially if elected through proportional representation, tend toward multiparty systems where even relatively small political groupings are represented in the legislature. As a result, distinct minorities can still participate in the political process at the highest levels of government. This diversity encourages dialogue and compromise as parties struggle to form a ruling coalition. Should the coalition collapse or the party lose its mandate, the prime minister resigns and a new government forms or new elections take place–all without a crisis threatening the democratic system itself.
The major drawback to parliaments is the dark side of flexibility and power sharing: instability. Multiparty coalitions may be fragile and collapse at the first sign of political crisis, resulting in governments that are in office for relatively short periods of time. The government may also find itself at the mercy of small extremist parties that, by threatening to withdraw from the ruling coalition and forcing the government to resign, can make special policy demands upon the government. Moreover, prime ministers are only party leaders and lack the authority that comes from being directly elected by the people.
Another concern is the lack of formal institutional checks on parliamentary supremacy. A political party with a large enough majority in parliament, for example, could enact a far-reaching, even anti-democratic political program without any effective limits to its actions, raising the prospect of a tyranny of the majority.
For presidential systems, on the other hand, the principal claims are direct accountability, continuity, and strength. Presidents, elected for fixed periods by the people, can claim the authority deriving from direct election, whatever the standing of their political party in the Congress. By creating separate but theoretically equal branches of government, a presidential system seeks to establish strong executive and legislative institutions, each able to claim its electoral mandate from the people and each capable of checking and balancing the other. Those who fear the potential for executive tyranny will tend to emphasize the role of the Congress; those concerned with the potential abuse of a transient majority in the legislature will assert the authority of the president.
The weakness of separately elected presidents and legislatures is potential stalemate. Presidents may not possess the votes to enact their program, but by employing their veto power, they can prevent the congress from substituting its own legislative program.
Presidents, by virtue of their direct election, may appear more powerful than prime ministers. But they must contend with legislatures that, whether or not controlled by the opposition, possess an election base independent of the president’s. Party discipline, therefore, is considerably weaker than in a parliamentary system. The president cannot, for example, dismiss or discipline rebellious party members as a prime minister usually can. A prime minister with a firm parliamentary majority is assured of passage of the government’s legislative program; a president dealing with a congress jealous of its own prerogatives must often engage in protracted negotiations to ensure a bill’s passage.
Which system best meets the requirements of a constitutional democracy: parliamentary or presidential? The answer is the subject of continuing debate among political scientists and politicians, in part because each system has unique strengths and weaknesses. It should be noted, however, that both are compatible with constitutional democracy, although neither guarantees it.