Four out of the eight candidates in Iran’s presidential elections are members of the Revolution Guards. However, ayatollah Rafsanjani, the frontrunner, has never been one. He is a conservative who adapts himself to prevailing trends.
The Revolutionary Guards were created in May 1979 because the religious suspected Iran’s Army was still in favor of the former regime and due to the fact that many of its officers had been trained by the United States. These forces had in courage and motivation what they lacked in strategy and tactic sense. This is the reason why they had so many losses during the war against Iraq. However, such a sacrifice made them as respectable as the Iranian armed forces and at the same time made it easier for them to have informal ties with the clergy. Today, Iran has two armies: the conventional armed forces in charge of protecting the territory and; the Revolutionary Guards to protect the achievements of the Revolution.
In several occasions, the Guards have threatened the civil government with wrestling power if the political leaders do not repress demonstrations. However, since 2003, they have adopted a more sophisticated strategy: taking control of the political power of the country through the Coalition for the Islamic Development of Iran. Nowadays, 90 Iranian members of the legislature have served in the Revolutionary Guards, as well as half of the presidential candidates. Military men are not necessarily good political leaders; but the guards have never respected the division between civil and military affairs.
An Iranian president linked to this organization is worrisome for it has connections with all armed Shiites groups of the region, from Lebanon to Iraq, and it wants the bomb at all costs. In view of such a situation, Rafsanjani is a more convenient solution though he is known for his repressive activities and his intentions to arm Iran.
For Iran, there are no good solutions in the short term.

Daily Star (Lebanon)

The reverberating impact of the Revolutionary Guards”, by Abbas William Samii, Daily Star, June 17, 2005.