I fear Trump will be a nightmare for the U.S. (but I hope I'm wrong and he exceeds my very low expectations), but I'm quite certain that he (and the Republican-controlled Congress, Supreme Court, etc.) will be a total nightmare for unions in general (about which I am very unhappy) and, in particular, the teachers unions (about which I have mixed feelings).
I am not anti-union – in fact, I think the precipitous decline of unionization in the private sector since ~1970 (from over 30% of the private sector workforce to under 7% today; it's been fairly steady at about 1/3 of the public sector workforce) has been a calamity for the U.S.: a major contributor to job losses, stagnating wages, widening income inequality, etc. – but I am for sure against teachers unions using their power to screw kids – like denying them high-quality charter schools (those in MA are the best in the country).