|You have to pick your battles. It is not feasible or wise to go to war with every country or group that poses some degree of threat to you, especially if they haven't actually attacked you.|
And, if you look at the actual threat to our citizens, the biggest threat by far is posed by Pakistan. They actually have nukes, and there is a serious threat of their government being taken over by extreme Islamic fundamentalists sympathetic to the Taliban. Iran, OTOH, while it has a fundamentalist leadership that oftentimes talks crazy, is governing a citizenry that for the most part adores Western culture and despises the theocrats ruling them. The Iranian government has to try and keep a lid on the possibility of the citizens rising up in revolt, which a pre-emptive war upon us without provocation would likely precipitate.
Given this much graver threat from Pakistan, one of the least wise things we can do is to have our troops stretched to the breaking point fighting three wars in Afghanistan, Iraq, and Iran. The smart thing would be to pull the troops out of Iraq, bring most of them home to rest up, repair their equipment, and prepare for the worst (whether the worst might break out in Pakistan, North Korea, or Iran), and send a few more troops over to Afghanistan to fight the Al-Qaeda rebels holed up along the Pakistan border, keep them busy so they are less able to try and destabilize Pakistan.
That is, we should stick to the NIOF principle -- fight the organization responsible for 9/11, and have well-rested and trained troops stationed on U.S. soil conspicuously prepared to defend ourselves against the many governments and terrorist organizations who want our citizens dead, but not engage any of them unless or until they pick a fight with us.