President Andrew Johnson wanted to have Lee put on trial for treason. Grant considered that a violation of the parole given to Lee at Appomattox Court House and threatened to resign from his position as General of the Army unless Johnson dropped the idea. Lee, for his part, never let anyone say anything negative about Grant in his presence.
Flood was asked about the story that when Lincoln was told that Grant was a drunkard, that he wanted to know the brand of whiskey Grant drank and he would send a barrel of it to each of the other generals. Turns out the story is not true--someone who had heard it told it to Lincoln and he denied having said it.
About 30 years ago Flood published a very good book on Lee's final years (after the end of the war).
Both of them were very interesting, powerful and flawed men.
Here, I have changed my little graphic to reflect that.
We should always remember that a person can be both flawed and great.