Eisenhower in War in Peace by Jean Edward Smith. My paternal grandfather was Harvey Isenhour, and his surname is pronounced the same as President Eisenhower's is, so I was interested to learn more about a President to whom I might be distantly related.
I was aware that Eisenhower had an affair during World War II, but wasn't aware of the extent of it until I finished this book. He basically kept her as a wife in Europe while Mamie, his actual wife, remained stateside, and then he abruptly dumped her when the war was over. That, of course, was a small part of his World War II story, and his overall story is even broader.
Eisenhower is part of the reason we have an interstate highway system. Early in his military career he was involved in an exercise to take a military convoy across the United States on what was then a very primitive road system, at least from our point of view. The difficulties the convoy encountered on that trip convinced him of the need for a national system of roadways.