Lyndon Johnson started that particular habit of political callousness (celebrating his own mano and mojo in the face of others' adversity) back in 1963.
John Kennedy's body was still cooling in the Capitol Rotunda, and LBJ was already holding meetings with his stoolies and stoogies and laying out his election run in 1964 and his legislative campaign for the next spring session of the Congress. Business as usual, IOW.