Aaarg! Rick Beard in the New York Times has a somewhat reasonable column about Antietam entitled the America's bloodiest Day. However, he persists in repeating Stanton slanders as if they were historical fact. So for the record:
1) There is no evidence McClellan "refused" to "reinforce Pope". McClellan was acting under Halleck's orders and was in Alexandria Va - 1 hour from the White House. Halleck and Lincoln were the "decision makers" - not McClellan. McClellan was in no position to "refuse" to do anything.
2) McClellan did not propose that "we leave Pope to get out of his scrape" - he told Lincoln that there should be no half-way measures. Either reinforce Pope with everything and have them "cut their way through" or "make the Capital perfectly safe". Two alternatives that Lincon and Halleck should decide on. McClellan ends his message by stating he would cheerfully and enthusiastically support EITHER course of action. But no half-measures.
3) There is no evidence that McClellan did anything to hinder Pope or do anything other than what he considered to be the correct military decision. There is no evidence McClellan was motivated by jealousy or was trying to sabotage Pope. Historians constantly quote these so-called "letters to his wife" completely disregarding that McClellan was "blowing off steam" or "venting" to his wife. I wonder what Abe was telling Mary Todd about McClellan, I wonder.
4) There is no evidence, other than Stanton's wish and Halleck's belief that McClellan was slow in evacuating the Peninsula, or dragged his feet, or delayed because he wished to hurt Pope.