From the electoral point of view, the main difference between the two main systems of government is that in a presidential government, magistracy consisting of one person is chosen, as opposed to a parliamentary government in which an assembly is elected, representative of all the political parties in the country and entrusted with the swearing in of the president of the government. The elements of the electoral system in each, therefore, are shaped in radically different ways.
In the presidential system, the election of the president usually is a national event in which all registered citizens' vote. It is always a majority vote, often demanding that the winning candidate obtain at least 51 percent of the votes cast. If necessary, a second round may be held among the best placed candidates from the first round.
Elections held within parliamentary systems, however, require the establishment of electoral constituencies (see Electoral Organisation), which do not correspond with the national territory as a whole, and leave room for very different solutions in terms of the form of expressing one's vote, as well as, above all, the electoral formula.
Another aspect that notably affects the attitude of the political forces in the face of elections, is the prohibition of re-election (or double re-election), characteristic of presidential systems. This limitation compels the parties in power to dispense with their best-known figure and periodically renew their leader much more often than in parliamentary systems. In the latter the logic is that whoever loses the election usually has the opportunity of trying again, so that renovation is always the consequence of an electoral defeat.
However, perhaps the most significant feature for the organisation of the electoral processes, is the varying degree of predictability of the elections. Presidential elections are held on pre-set dates, whilst in the parliamentary system, maximum periods of duration are set for the legislature, which can always be shortened at the unilateral wish of the president. Most of the time, this leads to the political parties and the electoral administration being surprised by the date of the general elections.
The influence of either of the models on the administration commissioned to organise the elections is evident.
Regular set announcements of elections permits all the necessary operations to be planned ahead.
The utilisation of the power of dissolution makes an especially flexible and effective electoral administration essential, able to organise the electoral processes within very brief periods envisaged in each electoral system (around two months).
A similar statement can be made with regard to the electoral mechanisms of each political party, with the added problem that it must select a sufficient number of candidates to participate in all the constituencies in the country, within the time between the announcement of elections and the naming of candidates.
