These are difficult issues that the United States has never fully confronted, in part because it would require asking hard questions about the utility of an Iraq war for which thousands of Americans gave their lives. While these issues do not necessarily suggest that Saudi Arabia had a hand in 9/11, it is easy to see how, to many Americans, that could end up feeling true. The 28 pages, regardless of what they actually show, are way of answering the unanswered questions and resolving the unresolved emotions that Americans have never quite collectively processed.
If there turns out to be any truth to the ties between Saudi Arabia and 9/11 it is almost certain that it will damage relations between the United States and Saudi Arabia. Even if there is no official problem between the countries, citizens of the United States are sure to harbor distrust.
If these documents prove to be true, I suspect that the relationship the United States has with Saudi Arabia may be greatly compromised. For a number of years, we have built up a trust between our two countries, and any Saudi involvement with 9/11 will likely come as a shock and disappointment.
It really depends on the extent of Saudi Arabia's involvement and/or support of 9/11. In analyzing their attachment to the attacks, it is also important to determine whether support of the terrorism was country-wide and involved Saudi leaders, or whether it just involved a small extremist group not representative of Saudis.