Effective governance relies not only on those in power but, almost as much, on those who oppose and oversee them. The electoral system should help ensure the presence of a viable opposition grouping which can critically assess legislation, question the performance of the executive, safeguard minority rights, and represent its constituents effectively.
Opposition groupings should have enough representatives to be effective (assuming that their performance at the ballot box warrants it) and in a parliamentary system should be able to present a realistic alternative to the current government. Obviously the strength of the opposition depends on many other factors besides the choice of electoral system, but if the system itself makes the opposition impotent, democratic governance is inherently weakened.
A major reason for the change to an MMP electoral system in New Zealand, for example, was the systematic under-representation of smaller opposition parties under FPTP. At the same time, the electoral system should hinder the development of a ‘winner takes all’ attitude which leaves rulers blind to other views and the needs and desires of opposition voters, and sees both elections and government itself as zero-sum contests.
In a presidential system, the president needs the reliable support of a substantial group of legislators: however, the role of others in opposing and scrutinizing government legislative proposals is equally important. The separation of powers between legislature and executive effectively gives the task of executive oversight to all legislators, not only the opposition members. This makes it important to give particular thought to the elements of the electoral system which concern the relative importance of political parties and candidates, alongside the relationship between parties and their elected members.