If you see your projects becoming increasingly insignificant, that is a significant development. You are not even permitted to ask questions, and this will ultimately undermine your productivity, satisfaction, commitment, and even your self-esteem.
Your manager is an obvious bully, and he senses that you are a willing target. When reacts with hostility, you back off. This downhill cycle is going to continue to roll until you speak up.
You need to meet with you manager, but not merely to express your dissatisfaction. He needs to understand that these petty assignments are costly to him and the department because they prevent you from providing adequate attention to the main events of your job.
If he goes into hostile mode, you should take a deep breath, speak slowly and clearly, look him in the eye, intersperse his name into your comments, reemphasize how you feel about these assignments, and then offer some alternatives, such as more junior level individuals who may actually learn something from these chores. His reaction is going to be revealing on all levels.
In terms of the bigger picture, he may be downsizing your job as well as your self-esteem in order to induce you to quit. Although it is important to look him in the eye, you should keep an eye out for other signs as well as other opportunities.
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