Several days ago a "powerful bomb" demolished a Shiite shrine in Iraq, and I couldn't stop myself from coming up with a conspiracy theory. I'm no expert, but pictures show thick cables sticking out, which, to me, means reinforced concrete. If that's the case, we're not talking about a stick of dynamite, or even a couple of artillery shells duct taped together; we're talking hundreds of pounds of explosives. Also, the dome seems to have been levelled completely flat at the top, which seems to imply equally distributed forces, caused by a centrally located explosive device.
If my assessment is correct (likely not, but stick with me here), this raises some questions. Who would be able to carry out such an attack? And who gains from such an attack? Unfortunately, the answer to both questions would be: the US.
The former case is obvious; we have the most capable military in the world, there's not much we couldn't destroy (well, fixed targets, at least). The second case requires a bit more of a stretch. The last few days have proven the incident to possess sufficient volatility to incite significant sectarian conflict. If the US is unable (or unwilling) to quelch such conflict, it is likely to lead to a messy, bloody, full blown civil war. This would definitely be a loss to US intentions, yet it would give us an exit strategy. If the administration were to say "We tried to bring them democracy, instead, they decided to fight themselves" the US public (and I'm talking about the same public that voted this current administration into office), would likely accept that as reasonable grounds for withdrawal (besides, Vietnam was a civil war --I think people still remember that). Alternatively, and perhaps more likely, a civil war in Iraq would compel the UN and the rest of the world to become involved in Iraq, allowing the US to relinquish control and responsibility. With sufficient international cooperation, there is also some chance of peace in Iraq, thus fulfilling a US objective that is clearly currently unattainable. Either way, the US gets an out.