2 Samuel 24:10
And David's heart smote him after that he had numbered the people. And David said unto the LORD, I have sinned greatly in that I have done: and now, I beseech thee, O LORD, take away the iniquity of thy servant; for I have done very foolishly.
1 Kings 15:5 (KJV)
Because David did that which was right in the eyes of the LORD, and turned not aside from any thing that he commanded him all the days of his life, save only in the matter of Uriah the Hittite.
This one pretty much speaks for itself. For an apologist to get out of this one, he has to maintain that (somehow) David "sinned greatly" in the matter of the census, but at the same time he "turned not aside" from the Lord's commandments concerning the census.