Disclaimer: I voted for him both times.
It isn't even a matter of manned vs. unmanned exploration. The Space Shuttle was the Universe's most cost-overridden project ( until the F35 came along). The original promise was that the materials scientists would produce a monohull insulating layer. The moment they gave up and announced it would take 70-zillion separate, custom "bricks" , the program should have been shut down. Heck, it would have been cheaper to shoot astronauts 3 at a time on Sat-Vs, shoot up some payloads & return vehicles (modded Apollo3s) etc. than what it cost to build and maintain the shuttle fleet.