So, if a major terrorist attack is successful on American soil in 2009, that will be entirely President Obama's fault? Should we then construct conspiracy theories about how President Obama schemed with Bin Ladin to justify whatever unpalatable policies might seem needed in the aftermath of that attack? Of course not, and the same should apply to your suggestion that President Bush's administration was responsible for not preventing 9-11.
The modern Radical Islamic Movement goes back to WWI when they chose the wrong side, and Britain signed the Balfour Agreement. During WWII, the Grand Mufti of Jerusalem was one of the most important Islamic leaders, and he was a devoted follower of Adoph Hitler. Whoops, the chose the wrong side again and at the end of WWII a conscience stricken world created the State of Israel. The ink was hardly dry, when the Islamic nations mounted a war of annihilation against the Jews. They lost, even though the little Israeli State was outnumbered and outgunned by their enemies. Israel found friends in the West, and the Islamic States became clients of the Soviet Union. Dang, can't they ever choose the winning side? They tried and tried again and again to bury Israel without success, and finally some Arab leaders got tired of the effort and tried to bury the hatchet. The militants didn't approve of Peace, so they assassinated Islamic leader who didn't toe the line.
When the godless Soviet Union occupied Afghanistan, even those who hated the West most bitterly were happy to receive the arms and support of the US. Finally, they picked an ally who could win. Once the Soviets were expelled from Afghanistan, the country became one of the most repressive Islamic States imaginable. The Taliban destroyed priceless ancient statuary, and imposed a form of Islamic Law that reduced women to virtual slavery and penalized men if their beards didn't meet some test. The Taliban were so confident in their position that they didn't even make much effort to hide their support for Al Queda's plans to expand terrorist operations onto U.S. soil.
Terrorist attacks carried out by various Radical Islamic groups began to increase shortly after the fall of the Soviet Union. Finally off the leash, terror bombings increased across southwestern Asia, around the Mediterranean Sea, and in Europe where large numbers of Arabic and Palestinian refugees had taken up residence. Aircraft and cruise ships were high-jacked by Islamic terrorists who murdered their hostages, and blew up their "prizes". Virtually from the moment that the Soviet Union fell, Intelligence agencies around the world began warning that Islamic terrorist organizations were going to become increasingly dangerous. The whole region was a tender box that led to the Iraq-Iranian War, followed by the invasion of Kuwait.
In the three to four years leading up to 2001, US Intelligence was warning Presidents and Congress that there was an increasing likelihood that a major terrorist operation would be attempted on American soil. That wasn't what the political leadership of the country wanted to hear, and was mostly ignored by Democrats and Republicans alike. Until it actually happened, no one wanted to believe that a successful terrorist attack inside the Continental US was possible. Even after several unsuccessful terrorist operations, the political leadership and the American public remained mostly complacent.
Given the history involved it was almost inevitable that a major attack would be successful, and it was. In the weeks after 9-11, otherwise sober people were calling for a nuclear response. Iraq had been assiduously painting a target on itself for years as it hedged and avoided compliance with the Cease Fire conditions that suspended the Gulf War. Saddam fostered the belief that he had, or would soon have weapons of mass destruction. He was openly calling for terrorist acts against Israel and the West. Iraq was a prime candidate as the covert sponsor of Al Queda. The other prime suspect was the Taliban in Afghanistan. Operations against Iraq were "easier" because of its geography and the fact that resumption of the Gulf War was justified by Saddam's actions. Operations against Fortress Afghanistan were harder, because of its remoteness and difficulty in putting sufficient military force on the ground to be effective. Pakistan gave us some very big help, and the newly liberated Soviet states north of Afghanistan let us insert small numbers of special forces through their borders. Overflights of Iran were discouraged, and that left Iraq as the nearest point where Afghanistan operations could be logistically supported.
President Bush didn't start this war with Radical Islam, they did. The Republican Party is no more responsible for the conditions that made 9-11, than the Democratic Party. Every administration going back to Wilson has some small share in it. And, all of them were doing the best they could. Past policies were sometimes strong, and other times week, but in the end its hard to see how things might have been different.
Now President-elect Obama will get his whack at the apple. Will he be strong and tough with the enemy, or will he dither and encourage them to probe for his weaknesses?