How can you tell when a politician is lying?

[Bapopik at AOL.COM]

"The good news is, he only lies when his lips are moving."
--Peter Vecsey on the squandered talent of recently released NBA player J. R.
Rider, NEW YORK POST, 19 March 2000, pg. 103.

   It's an old joke.  "Q: How can you tell when a politican is lying?  A: His
lips are moving."
   Incredibly, it's not in SAFIRE'S NEW POLITICAL DICTIONARY (that I could
see).
   I remember the line from before the ADS voted "Bushlips" as the Word of
the Year.
   I'll probably check Joey Adams's works on Monday, but does anyone have any
clues?