Bush joke

**Q: When is a Bush not a Bush?

A: When he’s A merkin!

(For further reading… Straight Dope answers: WTF is A merkin? )**

I don’t get it. Is that a play on the word “American”?

yup.
read the column: http://www.straightdope.com/classics/a3_232.html

The subject of the OP is a perfect example of redundancy.

he did add Bush to the equation which has double entendre. It may or may not be funny, but it’s at least somewhat unique.