Here is the best example of the effect of shore bombardment:
3 divisions of Marines are attacking 12 German infantry divisions. The -102.40 modifier reduces their defensive efficiency to 1%, which means (I think) only one out of every hundred shots that would have hurt the marines actually lands. The battle took three days but I only took 3 strength points of damage.
Note that shore bombardment goes away if enemy fleets engage your fleets. Note also that the supporting fleet is the entire USN - a dozen carriers and 2 battleships.
I didn't really cover Truman's re-election - there's no way he would have lost. Casualties are very hard to estimate; I would say anywhere from 350-500 thousand Americans fell in the three years I played.