Imagine a world war where the USA lost +5 millions soldiers to take north africa, middle-east, western and central europe.
Trice that many US soldiers where left crippled/wounded, be it by chemical, radiological or conventional warfare.
+7 years of total war, +1 millions civilian casualties to nuclear attacks(Hirosima-sized bombes) on major east-coast cities(New York 5, Philadelphia 3, Boston 3, Chicago 2, Washington 1, Buffalo 1), attacks no defences at the time could hope to intercept.
Despite that, roosevelt decided that the liberation of europe would go on, it left endless devastation very much similar or worst than OTL´s east front.
Paris and London looks pretty like OTL Warsaw & Berlin.
Germany itself has been left by the war in a near pre-industrial state, the Rhineland has beenm left a vaste field of rubbles and metal scrapes. Occupation of it is mostly upp to the USA as England and France have been bled white and their governement structures have been mostly destroyed, soviet-union occupies everything left east of Berlin/Prague/Vienna (which are reduced to bombed-out shells).
How would all of this affect mentalities, atitudes in the USA?