Troubling means: causes distress or anxiety. For example: "The question was troubling" means that the question caused the person who heard it to be distressed or anxious. So, in this context "This question was never more troubling", it means that the same question has been asked and heard before, but this time, the same question causes anxiety. For example: the president may be asked a lot "what should we do about this problem?". However, if the president is asked that when the solution to the problem could have serious effects, such as war, for the president, that question had never been so troubling - before if you asked, what should we do about the problem and the problem was what to cook for dinner, there would be nothing troubling about the question, however, this time, it causes anxiety.