Josh Marshall points out that bin Laden was trapped at Tora Bora and surrounded. But Bush was so focused on attacking Iraq that there were not enough troops available to capture or kill bin Laden when we had him.
The CIA commander, Gary Berntsen, in charge of CIA operations at Tora Bora wrote his book, Jawbreaker and clearly explained that we had bin Laden, we knew he was there, but let him go free. This is Bush's fault. Whether it was intentional, for political purposes or simply incompetence really doesn't matter much. Any or all of those motivations are possible, but it will never be known which was most important. The motivation doesn't matter. The action makes it Bush's fault.
Josh Marshall refers to the shorter Newsweek article that explains what "Jawbreaker" said.
This failure at Tora Bora was, of course, the failure that Gen. Tommy Franks got his Medal of Freedom for keeping quiet about. George Tenet (CIA Director) got his for not telling that the CIA had carefully and repeatedly told Bush, Cheney and the White House staff that Saddam had nothing to do with 9/11, did not have WMDs and was no major threat to the U.S.
Franks and Bremer were two of three. At the same presentation, Jerry Bremer, who was the man in charge of the Coalition Provisional Authority (CPA), got his Medal of Freedom for not telling who instructed him to disband the Iraqi Army and conduct the deBaathification of Iraq which worsened the occupation quite rapidly, as well as so many other screw-ups that were conducted by the CPA.
It's hard not to just keep going when describing the myriad failures and even treasons conducted by this administration. But letting bin Laden go free when he was in our grasp is one of the very largest screw-ups or treasons.