Driftglass wrote a wonderful piece about the differences between the Left and Right over the last 40 years.
I could go on -- endlessly (as if I haven't already :-) -- but the point is this: there is no bigger, more destructive and more commonly repeated lie in American politics today than "Both Sides Do It". Nothing else even comes close (all of the Right's gigantic, treasonous lies about Iraq, for example, eventually had to give grudging way to the realities of the catastrophic losses and failures to which that enterprise was doomed.)
Of course, none of the Bush Administration's various war criminals and Useful Idiots were ever docked so much as a day's pay or an erg Beltway prestige once their lies caught up with them (in fact a disturbing number of America's leading Neoconservative traitors actually leveraged their treachery into lucrative career advancements). And of course once the Bush Administration's staggering concatenation of fraud, failure and lies started to blow in their faces, the party bosses had a whole new suit of lies ready and waiting to replace the old, worn out ones.