On stage Wednesday in Michigan, Perry could only come up with the names of two of the three agencies he had promised to get rid of if elected president. He ended by saying "oops."
Perry later said he would eliminate the Commerce, Education and Energy departments.
Thursday night, Perry appeared on the "Late Show with David Letterman" to deliver a "Top 10 Rick Perry Excuses" for the gaffe.
- "Actually there were three reasons I messed up last night. One was the nerves, two was the headache and three was, and three, uh, uh. Oops."
- "I don't know what you're talking about. I think things went well."
- "Hey, I was up late last night watching `Dancing With the Stars."'
- "I thought the debate was tonight."
- "Hey, listen. You try concentrating with Mitt Romney smiling at you. That is one handsome dude."
- "Uh, el nino?"
- "I had a five-hour energy drink six hours before the debate."
- "I really hoped to get on my favorite talk show, but instead I ended up here."
- "Hey, I wanted to help take the heat off my buddy Herman Cain."
- "I just learned Justin Bieber is my father."
The Texas governor is trying to turn the stumble into an opportunity. He is asking supporters to pitch in a few dollars for every agency they would abolish.
The Associated Press contributed to this story.