Moore: Liar and Libelous?

InstaGuy refers us to Spinsanity’s fact checking of Michael Moore:
“Moore has apparently altered footage of an ad run by the Bush/Quayle campaign in 1988 to implicate Bush in the Willie Horton scandal. Making a point about the use of racial symbols to scare the American public, he shows the Bush/Quayle ad called “Revolving Doors,” which attacked Michael Dukakis for a Massachusetts prison furlough program by showing prisoners entering and exiting a prison (the original ad can be seen here [Real Player video]). Superimposed over the footage of the prisoners is the text “Willie Horton released. Then kills again.” This caption is displayed as if it is part of the original ad. However, existing footage, media reports and the recollections of several high-level people involved in the campaign indicate that the “Revolving Doors” ad did not explicitly mention Horton…”
Maybe I’m over-using my old Communications Law class knowledge, but couldn’t a legitimate case be made that this is, therefore, a libelous and actionable accusation on Moore’s part against Bush? I would think that demonstrating potential harm would be feasible; and doesn’t Moore altering the tape to make it appear Bush said something he didn’t constitute the kind of “false statement” to which libel law would apply?
Put more generally: does altering and re-broadcasting a statement made by another person in a way which might cause damage to them constitute libel?
Legal eagles of the Blogosphere: little help?
PS – Crap. It’s likely slander, not libel, isn’t it? Too late to change now; I’ll just sit here and wonder how I ever passed that Comm Law course…