Actually, MacArthur overestimated Hapless Harry Truman’s manhood.
Oh, that's right, he wasn't caught flatfooted when a million Chinese came across the border!
He then ran to Truman and wanted him to nuke the Yalu!
But as Gen. Bradly stated, Korea was the wrong war, at the wrong time with the wrong enemy, so we were not going to start WWW3 there.