Shall I continue?
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.--That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed...Now, substantively, this is half of the crux; the other half being what happens when Government is Destructive of those ends. I’m not sure I want to talk much about that substance; it seems straightforward and correct. I should say, correct philosophically. I don’t think that Governments have been instituted most often to secure Rights, either for individuals or for populations. I do think that Governments ought to be instituted for those reasons, and that the powers of Government are most likely to be just when they derive from the consent of the governed. I think that the Government we eventually set up was, mostly, set up in order to secure rights for its citizens (not the inhabitants) and the justice in its actions, which was (in my opinion) far greater than the justice of its near contemporary states, derived from the willing consent of a larger portion of the governed than was usual.
In fact, what’s interesting is that the language here is difficult to place in context. Is Mr. Jefferson (along with his colleagues) saying that this is what a Government should be or what Governments are? Are they speaking as natural philosophers, from historical evidence, or as speculative philosophers, from their asses? The language, to me, implies that they are speaking from historical knowledge. Of course, they don’t provide specifics, the way they might if they were arguing from history. The tone is slippery. They use the present tense; is it the historical present, or are they distinguishing modern governments?
What’s going on, I think, is a sort of blending, where the writers imply a sort of historical authority (even inevitability?) to their Declaration, while simultaneously making a break with older, out-of-date ideas of Government. Again, a small farmer might well be taken aback by a bold statement that the Government’s just authority derives not from Divine guidance or selection, nor from a kind of meritocratic aristocracy, not from the superiority of the governors deriving from superior education or superior breeding or superior morality, not from tradition, not from history, not from anything but the consent of the governed. It’s not a brand new idea, by any means, but it is a radical idea, and not necessarily an idea that is, placed alone and conspicuous, necessarily trustworthy. However, the writers have already claimed a magnificent and broad authority (unanimous, necessary, Nature, Gd, entitle, decent, impel—all in addition to the obvious erudition, the calm reasonableness of the tone, and the philosophical context) that lends support to the idea.
Try it the other way, without the props, without nodding your head to everything that went before. What is government for? Who or what authorizes it? I think (I hope) you will come up with something close to Mr. Jefferson’s formulation. Most of the world rejects it. I hope that the ideas are persuasive enough to be spreading among populations domestic and foreign. Any rhetorical help we can get from today’s Jeffersons would be nice. Apply at the front desk, Gentle Readers.
chazak, chazak, v’nitchazek,
-Vardibidian.

Jefferson, I’m not.
A couple of things here. I think the word “just” in “deriving their just powers from the consent of the governed” is key. This way, you can argue that it applies to all historical governments; whatever powers they had that didn’t derive from the consent of the governed were, presumably, not just.
Also, there’s an argument to be made that all governments really do derive their power, ultimately, from the consent of the governed, in that the government has that power until the governed revolt. As often happened, historically. So we could say that democracy isn’t fundamentally different, except that by putting the consent up front, we avoid a lot of bloodshed. Plus the governed have to get a lot madder to revolt than they do to vote the current rascals out, so they suffer more in the interim.
I would get into a tautological muddle, then, unless you can really look at historical governments and whether their powers are just without applying back to the consent of the governed. Were the Greeks just? Was Henry II? Was King John? What is justice? But it’s a good point that, one way or another, Mr. Jefferson (and his colleagues) clearly meant just to be the key word in that phrase, both to point out the injustice of King George and to imply a promise of justice under the new revolutionary government.
I find the argument that the governed always consent to be a touchy one. In an unequal society, the governors can impel the consent, or at least the acquiescence, of the governed for a long time. A people in slavery is still governed. There’s the further question (and Mr. Jefferson sidesteps this one) of how many of the people need to consent, or at least of how big a segment can be compelled to acqueiesce. Slaves? Women? Disgruntled Tories? Communists? Anarcho-syndicalists? Clearly, the government can maintain what we think of as “the consent of the governed” even if a few hot-heads would like to tear it down, but when does the category of hotheads get so large (or so correct) that a minority witholding consent de-authorises the government, under this scheme?
The fundamentally different thing to democracy is that it requires the willing and explicit consent of a very large portion of the governed, and it defines the governed fairly inclusively. King John ruled at the explicit and willing consent of the governed, but the governed were the local nobles (as I understand it). The consent of the rabble was irrelevant. I’m not sure that Mr. Jefferson sees the rabble as relevant, but the bourgeousie (which King John didn’t have to deal with) are relevant, and get to consent.
Thanks,
-V.