Allan Pinkerton, Chief of the Union Intelligence Service, with President Lincoln
Here is some of what Pinkerton said about McClellan:
"From the time of his commission to the day when he was relieved, after his splendid victory at Antietam, I followed the fortunes of General McClellan. When secret enemies were endeavoring to prejudice the mind of the President against his chosen commander; when wily politicians were seeking to belittle him in the estimation of the people, and when jealous minded officers were ignorantly criticising his plans of campaign, General McClellan pursued his course with unflinching courage and with a devotion to his country unsurpassed by any who have succeeded him."