I think its a bit of all of the above, because key to the situation is that Bush has time. The EU and other middle eastern countries are watching Iran closely as well, and don't want any sudden moves. There will not be a diplomatic solution from Bush unless it's the iron fist in the velvet glove approach. Putting the economic and financial squeeze on PM Ami in Iran is slowly producing dissent within the population as well as with the ruling religious class. The Iranian PM is being reigned in, and will continue to be if Bush wrachets up further sanctions.
From a military perspective, The U.S. is building very expensive mega-bases in Iraq in the country-side - indicating a longterm presence in the country. Over time they must secure the borders of Iraq, abandon participation in the civil war & turn swift attention to the Afghanistan-Pakistan border. The Taliban and Al Qaida must be dealt with - even if it means a swift and merciless purging of the western Pakistan provinces from which they operate.
Having done this there will be no need to actually invade Iran, because they will be sitting there shitting themselves about what the U.S. "could" do. Deterrance is good.