What have been Bush's biggest policy decisions?
Did he miscalculate on these decisions?
Should he be held accountable?
Should Congressional Republicans also be held accountable?
Was his major policy policy decision perfect? NO. Were any president's? NO.
So what were Bush's greatest miscalculations?
I would not characterize it as a miscalculation.
There was a choice in the Iraq invasion. Go with the troops that they had, or attempt to bring in more troops. The only way to do it would have been to enter, advance to the Euphrates around Nasiriyah, with the Marines and the 3rd ID. They stop and wait for the 4th ID to unload. They didn't have enough port facilities in Kuwait to deploy both at the same time. Then, with about 25%-33% more forces, they take Baghdad in one enveloping movement, basically keeping the Iraqi Army/allied groups from melting away.
Couple of problems. It takes two-three months to get the 4th ID up to Nasiriyah. 3rd ID and the Marines get to sit in the middle of the desert for all that time, while being attached basically by command type raids. While there would be more troops to secure areas, there would be more time for Ba'athist/Islamists to prepare. It is fairly likely that the there would have been much heavier causualties at the opening. We might have talking about 2-3 thousand dead on the road to Baghdad.