It’s not impossible to imagine an outcome in which Keystone XL would have survived to live its life to the fullest. However, the project was barely conceived before spin doctors diagnosed at least two major flaws that would prove to be fatal: timing and politics.
What is the meaning of 'spin' here? Is it a noun?
It's a noun. In this context, "spin" means "propaganda loosely based on facts". The idea is you "spin" the truth, distorting it into a convincing lie. Wikipedia has a pretty good article on it.
I have never heard of the term "spin doctor" before, but it appears that it means:
A person who publicizes favorable interpretations of the words and actions of a public figure, especially a politician.
