President George H. W. Bush was priceless with his remark about Chevy Chase and Dana Carvey imitation.
Msnbc has it although I am having trouble linking it here. The best I can do is the page that the link is on
http://www.msnbc.msn.com/id/16393733/
Scroll down to video (middle right) and there's a link to Wouldn't be Prudent