Your comment is rather US centric. I doubt the attack on the WTC is a main factor in the decline of democracies across the world.
I'm gonna challenge this assertion. I would actually assert the opposite: that trust is one of the worst poisons.
Why? Because trust breeds weak restrictions (checks/balances), and weak restrictions are easy for dictators to exploit, thus undermining democracy.
Rather, I say you want those in a democracy to assume everyone (including everyone within their own party) is a potential tyrant and to structure (and enforce) the restrictions accordingly.
Where the US in particular has really fallen down, in my opinion, has been the enforcement of those rules upon those in office because of partisan favoritism. Perhaps those showing favoritism haven't realized that in the bigger picture, although favoritism is convenient, it undermines the whole system in the long run.
I am not located in the US and there is no law that declares it mandatory in my country, but there is a political culture that a successor administration doesn't reverse the policies the predecessor has enacted in the previous term. That is to give it a chance to have an effect. There can be exceptions of course but there is a general understanding and it is regarded as good conduct to adhere to it. Honor amongst thieves perhaps, but it doesn't have to always end in nepotism.
Xenophobia, racism, and war are deeply routed in the culture, and date far before 9/11. We're simply witnessing the culmination of the slow erosion of checks and balances over centuries, which has exposed the raw flaws that have existed since the beginning.