There is evidence that certain members of the Pentagon have been interested for some time in the destruction of the Islamic Republic. Certainly many people and organizations would have their interests served by the removal of the Islamic government.

Just as the War in Iraq was mainly about securing oil supplies and US power in the middle East, A US invasion of Iran would have the same benefits.

However, I believe the Pentagon planners are aware that a US invasion and occupation of Iran in the near future is unfeasible.

Reasons that an invasion will likely not take place:
1) Iran is significantly larger and more populous than Iraq and Afghanistan, which have both proven difficult to control and occupy.
2) Iran has a much more effective government than Iraq or Afg. had--Iran is actually a kind of democracy, with established command and control, military cohesiveness, and competent leadership.
3) iran has a more diversified economic and industrial base than Iraq, with a maturing military industry..meaning that Iran has the capabilities to be self-sufficient in an extended conflict.
4) Geographically, Iran is more varied and rugged than Iraq, with many areas of high mountains, forests, desert, etc. An assymetrical insurgency would be even more effective in Iran than in Iraq.
5) there is even less support internationally for a war with Iran than there was for Iraq; I doubt a single nation would support the US.
6) The current administration has spent all it's political capital and no longer has the popular authority to conduct such a war.

In short, if the Pentagon and the Administration have any sanity whatever, they will not attempt an invasion of Iran at this time. Such an act, if carried out unilaterally by an executive order, might well result in domestic civil strife, impeachment, even revolution. I also think some military commanders might refuse the order, preferring to resign.