Pardon my question here as it probably has already been answered. Why wasn't OO Howard taken out of corps command? I have heard and read lots of historians and they don't seem to have a favorable opinion of his performance or his personality. Seems to me that if he was really that bad, wouldn't he get replaced?
Howard was many things. He was overall a poor corps commander, as seen at Chancellorsville, Gettysburg, and Pickett's Mill. However, he had several qualities that kept him around, for both respectable reasons and some less respectable ones.
First, the man was a hardcore Republican. The army was full of conservatives, such as McClellan, Rosecrans, and Hancock, many of whom had little interest in promoting the Republican agendas. Howard was one of the few West Point army officers who was a staunch abolitionist. Thus, he was needed politically to balance out the Democrat dominance of the army.
Aside from this side of politics, Howard was a brave man. He had lost an arm in a charge at Fair Oaks, was in the thick of the action on Cemetery Hill, and was wounded again at Pikcett's Mill. He may not be as brave or charismatic as a Barlow, Custer, or Gordon, but he had some respect from his fellow officers for his personal courage.
Finally, when he's sent west, Sherman (an arch-conservative by any stretch of the definition) seemed to take a liking to Howard, and when Howard's corps was disbanded, appointed him to command IV Corps. I've heard from Sean Chick this was done out of a sense that, as a disgraced officer, he would not pose much of a political threat to Sherman. However, i get the feeling Sherman found him personally amiable, despite being on the far opposite end of the political spectrum, for he appointed him to replace the deceased McPherson in command of Sherman's Army of Tennessee (his prized force). In this capacity, Howard actually improved spectacularly in skill, and won victories at Ezra Church, Jonesboro, and lead half the army in the March to the Sea and into the Carolinas.