Eric Martin notes an excellent article by Nazila Fathi in the New York Times discussing what appears to be a widening rift between Iranian president Mahmoud Ahmadinejad and Supreme Leader Ayatollah Ali Khamenei:
In the past, when Mr. Ahmadinejad was attacked by his political opponents, criticisms were usually silenced by Ayatollah Khamenei, who has the final word on state matters and regularly endorsed the president in public speeches. But that public support has been conspicuously absent in recent months.
There are numerous possible reasons for Mr. Ahmadinejad’s loss of support, but analysts here all point to one overriding factor: the United States National Intelligence Estimate last month, which said Iran had suspended its nuclear weapons program in 2003 in response to international pressure. The intelligence estimate sharply reduced the threat of a military strike against Iran, allowing the Iranian authorities to focus on domestic issues, with important parliamentary elections looming in March.
Eric takes Fathi’s argument into consideration within the context of this past weekend’s tense naval standoff in the Strait of Hormuz:
The diminishing fortunes of the respective Iranian and American hawkish sets does certainly add an interesting backstory to the recent showdown in the Strait of Hormuz - as discussed yesterday on this site. There is a definite possibility that one or more groups was/is trying to, once again, ratchet up tensions in order to reassert relevance and influence.
Ahmadinejad is beginning to feel domestic backlash exacerbated by a woefully lagging economy — an economy he was initially elected to revitalize. As Fathi argues, without an outside distraction to keep Ahmadinejad relevant to his domestic constituency there is little hope for him. Combined with Khamenei’s newly softened rhetoric, Ahmadinejad is finding himself in an extremely precarious situation. However, if the Bush administration attempts to make up ground it lost following the release of the NIE with general belligerence, Ahmadinejad will undoubtedly find renewed political life and relevancy through his ability to set the agenda on external threats once more going into parliamentary elections.
I think it is important to note that the Supereme Leader of Iran, not the president, is the commander of the military forces, including the IRGC. It seems unlikely that Khamenei would have knowingly allowed the provocation in the Strait of Hormuz with it timed so closely to his public gesturing toward the United States. Ahmadinejad, however, could have made some calls — his involvement with the founding of the IRGC’s Quds Force in the `80s is fairly well known and the IRGC is certainly not at a loss for Ahmadinejad-style hardliners. If true, the Hormuz incident was an incredibly brash maneuver on Ahmadinejad’s part, aimed at maintaining his relevancy at the potential cost of Khamenei’s future support. This is what political desperation looks like in the Islamic Republic, a scary thought to be sure.
With the United States mired in Iraq, Iran finds itself in an extremely powerful position. Its influence over the Shi’a parties in Iraq allots it the ability to directly affect the outcomes of the American mission in the country. The SCIRI is particularly close to Iran, as it took refuge under the Islamic Republic during Saddam Hussein’s reign and its Badr Organization militia was trained by Iran’s Islamic Revolutionary Guard Corps. The al-Da’wa party was also housed in Iran for a number of years during its struggle against Hussein’s Ba’athist regime.
Military power plays a vital role in Iraq – in actuality, it plays a number of roles currently, which is at the root of the problem. Military force should only be used in order to attain military goals, generally being either the attainment or defense of territory, and/or the destruction of enemy forces. In Iraq, however, the administration is utilizing force to destroy Iraqi insurgents, defend the Green Zone, and affect political outcomes within the Iraqi system by acting as a counterbalance for Prime Minister Nouri al-Maliki against rival Shi’a parties and their militias, as well as Sunni insurgents. 
Iraq, originally cobbled together by acts of the British Empire after centuries of Ottoman rule as three, ethnically-separated governates, is experiencing the severe pangs of nationalism in the form of a bloody civil war. The Kurds, Shi’a, and Sunni are re-enforcing their regional boundaries as sectarian violence continues throughout the country, forcing even those who had once ethnically co-mingled during the Ba’athist regime of Saddam Hussein to flee to the relative safety of ethnically-defined enclaves. In the middle of this civil strife are the American armed forces, whose initial military victory – the deposing of Sadam Hussein – seems distant and ineffectual in hindsight’s prevailing clarity.