“The mullahs are going to have to roll the tanks or they are done.”
The tanks were mostly in the regular Army, which refused to fire on demonstrators in 2009. Most of the IRGC (Republican Guards, or Pasdaran) are specialty troops for rocket/missile units, naval, and exporting the revolution outside the country (Quds Force, Ramazan Corps). Many of their personnel are also dedicated to smuggling and other money-raising operations. Nowadays, the IRGC has re-focused on warfighting outside the country - and a lot of their combat power is now deployed in Syria and Iraq.
The IISS Military Balance (2007) says the IRGC has 125,000+ personnel and controls the Basij on mobilisation. The Basij are (at least in theory) subordinate to, and receive their orders from, the Iranian Revolutionary Guards Corps and current Supreme Leader Ayatollah Khamenei. However they have also been described as “a loosely allied group of organizations” including “many groups controlled by local clerics.” It is estimated that there are 90,000 active and 300,000 reserve Basijis. The IRGC also has new units of several thousand foreign mercenaries (mostly Afghan and Pakistani Shi’ites) fighting for them in Syria.
In 2009, the Basij needed to be reinforced with foreign militias like Hizbollah from Lebanon, and even so, they needed to pull in their forces from wide rural areas to be able to suppress the demonstrations in a few cities. Hizbollah has been badly bloodied in Syria, and is heavily committed there now.
Protests seem to be more widely distributed this time, and regime assets more stretched out and over committed.
Iran only has the GDP of Alabama, spread over 80 million people, with a huge percentage spent on foreign wars, an expensive nuclear program and widespread systematic government corruption. That regime is not 10 feet tall - they have a limited capacity in terms of how much they can handle at once.
They also have a very centralized chain of command and control - which is a center of gravity of their whole regime. If that gets impeded or overwhelmed, the whole security apparatus could freeze up or dissolve. One bullet at the right time could change history.
Interesting info. Over deployed with a soft under belly. Will be interesting to see how Putin responds.