He needn't worry. He's in no danger of it.
In fact, he's down there with Jimmy Carter, Bill Clinton, and Warren Harding right now.
So far--Jimmy Carter's still the worst President in U.S. history, even beating out Clinton and Harding, which is saying a lot!--but if Bush's refusal to enforce U.S. immigration law should result in a national catastrophe--e.g. a terrorist attack or the permanent empowerment of the decadent, corrupt, anti-American Democrat Party--Bush just could replace Carter.
I really think you have to include Woodrow Wilson in the list of worst presidents.