When: not sure. Probably some time around the late 80ies/early 90ies.
What: the political, i.e. the idea that there is a special realm for debate, not identical to any of the following: the legal, the economic, the military; in fact a realm in which any of these can negotiated and binding decisions concerning all aspects of living together can be made.
How: again, the exact circumstances remain obscure; as causes have been cited: the end of the Soviet Union, the economic crisis of the late 80ies, the internet and many more. In fact the reason is more likely that people simply grew tired of the political and stopped looking after it.
Signs: A tendency to present issues in public debate as a) having ONE solution and b) best left to the experts (economists, judges, think-tanks of various kinds). The thought that at least some of these issues could be resolved through negotiation has disappeared from public perception. A tendency to present opponents in debates not just as mistaken about particular points but borderline insane. A tendency to expect politicians to be smooth administrators, implementing measures we already all agree about.
Problems: Why should we care? Wasn’t ‘the political’ the leading cause of death in the 20th century? Why should we be concerned about the loss?