I am 74 and never heard of american exceptionalism until about 1 1/2 years ago....who started it...
I am 86 and from my time in a parochial grade school as a son of immigrants I remember being told that the USA was an exceptional government created by the Founders. My brother who was killed on Okinawa and myself who also served overseas in WWII went into service believing such. Perhaps one can take issue with the specific word expression ‘exceptionalism’ but I will argue the meaning of being exceptional is valid. That is at least until a bunch of immigrants and non caring citizens started being/thinking otherwise.