The expression, which has been around for quite a while, is brilliantly parsimonious. In just four simple words (really only three, since one of them is “to”), it succinctly encapsulates the left’s view–both of itself, and of the way the world works.
First, there’s “truth.” One of the hallmarks of much leftist thought is the idea of their own moral (not just doctrinal or analytic) superiority. The left’s definition of “truth” often seems to be that it consists of whatever they believe to be true. Ergo, whenever they “speak” (word three), it’s “truth” by definition; they certainly don’t need no steenking facts cluttering up their truth (as in the pesky Memogate).
Next, there’s “power.” The left is all about power differentials. Third-world countries or those perceived as powerless are always right (i.e. “truthful”); powerful countries are always wrong. It’s not, of course, just about international relations and countries, it’s also about people and economics: poor people=good (powerless), rich people=bad (powerful).
Want to know the origins of the phrase? I did; it turns out it has to do with Quakers and pacifism, (see this), a subject I plan to tackle some time in the not-too-distant future.
If Rather sees himself and CBS as an example of “truth,” particularly after Memogate, I’m not exactly sure what falsehood would be. The MSM and CBS are certainly also examples of power, too; hasn’t Rather ever heard of the expression “The pen is mightier than the sword?” (I know, I know; CBS doesn’t use pens much any more–or typewriters either, for that matter, unfortunately for CBS. But the expression is metaphorical anyway).
[ADDENDUM: In an attempt to head off possible misunderstanding, I will add that I am not talking about liberals here, I'm talking about the left. And I'm not saying Dan Rather is an example of the left; that's why I was a bit surprised to read that he'd used the phrase.]