Impression begins at the 2:26 countdown timer. Check out the crowd response. Carvey goes after the professorial tendencies of the President, nice contrast with Reagan and Bush. (Warning that the volume is set high and a commercial will play before the clip starts... but I guess NBC makes that the price of providing an easily embedded clip.)
Notice how he zings the President for being ineffectual. Check out the set up, then the punch line...all in good humor...but the message is there. Masterful.
This reminds me that Bill Maher used do political humor too. Then he just got mean. Dana Carvey shows how it's done.
UPDATE: Welcome visitors! I have achieved hobby blogger Nirvana... linked by Instapundit and Hotair in the same day. Awesome. This is my second link from the good professor, the first was my post on our "Angry President"