Here's an idea for how Obama can both hit back at McCain's distortions (e.g., his lies about Obama's tax plan) and continue to draw attention to his bizarre "misstatements" on matters of fact.
Obama can't just say "he's lying". Even if true, this statement is always perceived as harsh and negative. (Remember Bob Dole's "tell [Bush] to stop lying about my record"? He instantly fell behind and never recovered.) I don't say that others---like us---shouldn't call McCain a liar whenever appropriate. But Obama himself can't use that word.
What he can say instead is this: "The Senator's memory is at fault."
This phrase used to be the polite way of saying "you're a liar" in the days when "liar" was literally a fighting word---the response might be a challenge to a duel. On the surface, attributing McCain's mistakes (deliberate or not) to a trick of memory is a gracious and unobjectionable response.
I presume I don't have to point out the underlying point being made.
Notice that the precise wording is important. Obama must not say "McCain's memory is faulty"; that's over the line because it refers to memory in general, not memory in a particular instance. And god forbid he would ever say "McCain's memory is failing". He should pick one formulation and stick with it, possibly adding "again" now and then: "Senator McCain's memory is once more at fault." An acceptable alternative might be "The Senator's memory is misleading him." Any other ideas?
In particular, Obama needs something like this during the debates. He must have a forceful but politically correct (in the strict sense of the phrase!) way to call attention to lies and gaffes, one with as devastating an effect as possible. And it should be the same phrase over and over, the same way Reagan crushed Carter with his repeated "There you go again, Mr. President".
Maybe this is a bad idea; certainly I don't know how to get it to Obama for consideration. But what else should he do about the bullshit coming out of the McCain campaign? People hear the lies and believe them; they don't hear the corrections. Lying works; remember Kerry and the Swiftboaters. How else can we fight back?