Try again. Previous presidents made changes they were specifically empowered to make by act of Congress. But Mr. Obama's usurping of Congressional powers in the matter will be wholly without precedent, and a direct violation of the Constitution.
In other words, those who cite those alleged precedents for Mr. Obama's unilateral action on immigration are lying in their teeth. What they other presidents did wasn't unilateral.
Congress had authorized them to do as they did. It has not so authorized Barack Obama.