Glenn Greenwald, A genuine political sea change?, Salon.com, 28 April 2007.
(The letter from DCLaw1 that Greenwald mentions appears on this page.)

Some video evidence of this:

Sen. Mike Gravel at the South Carolina Debate, 26 April 2007.

Steven Colbert's amazing (amazingly funny, but too true) performance at the White House Correspondents' Association Dinner, April 29 2006: Google Video.

See also the episodes of Bill Moyers Journal noted previously.