The thing that has always made americans ignore the country's behaviour abroad has been the consistent social improvement at home. They could say "well things are getting better for me" and that enabled ignoring imperialist foreign policy. On top of that it provided the excuse for that policy because at home things were always getting better and therefore they would bring that to the rest of the world.

Now that's gone and with it people slowly become unable to ignore the foreign policy being evil and the excuses for it bullshit.