Discouraged from giving A's, but students are doing excellent work, what can a professor do?
Take special care defining the rules, previously, and stick to them. You should have a specific list of objectives and the associated grades. This is implicit on tests, more explicit on projects. For instance, when elaborating written exams, I usually try to cover the whole syllabus (for that part), with questions of different difficulties, for instance, 4 questions, one easy, two moderate, one harder. That way I can easily see who really knows the content and who is just coasting by...

If a student reaches all predefined objectives, that person earned an A. And you can easily prove it by showing that he indeed reached the objectives. It would be highly unethical not to give a deserving student an A for political concerns of some suit....