Looking at the big picture:

Given:

1. In Iran, the position of president has little actual power.
2. The real power is held by the Council of the Guardians, headed by the Supreme Ruler.
3. The Supreme Ruler controls the Iranian Islamic Revolutionary Guards.
4. All candidates for election were approved by the Supreme Leader.

Therefore:

5. Mousavi cannot make any real change in policy.
6. Mousavi was approved by the mullahs.
7. Mousavi is not seen as a threat to the regime.

Possible outcomes:
7. The regime will “relent” and accept the election of Mousavi, playing the people for fools.
8. The regime will use this crisis as an excuse to crack down hard on opposition and declare martial law enforced by the IIRG.