While in no way diminishing the astonishing accomplishments of the Lewis/Clark expedition, the plain fact of the matter was that the Louisiana territory would have been explored sooner or later, probably sooner, in any event. There was no perceptible shortage of pioneers, adventurers, opportunists, and/or traders in the U.S. in 1803. Jefferson deserves the credit (with not a little prompting from several Western politicians, btw) for commissioning the exploration, but can hardly have expected the cornucopia of discovery that unfolded. Again, a bit of good luck -- not despising luck, mind you, but let's not confuse lucky results with ''greatness'', however defined. By applying that sort of standard, one might have to conclude that the odious Bent Willy was ''great'' because he was bloody lucky enough to infest the office just as the major effects of the Reagan tax cuts were being felt throughout the economy.
The president who never gets enough credit IMNNHO (besides Coolidge, of course), is Madison. Jefferson left him a domestic economy in near-shambles, a Federal budget in almost complete disarray (read Nevin, among many others, for a description of this ugly situation), and with a trade war (essentially) with Britain. By the end of his term, Madison had resolved the trade war VERY favourably, somehow had managed to win that silly war that resulted from the trade war (hardly a mean feat, Britain being what she was at the time), had quelled the New England separatists, had initiated much more advantageous funding procedures (the banks' loan-origination fees in that day were stunningly outrageous, and Madison, while not completely able to stop their practices, curbed them rather sharply by introducing them, quite involuntarily, to the concept of competition), and -- by dint of NOT intefering much -- had seen to getting the economy back onto something resembling an even keel. Significant accomplishments indeed for the president of a 20ish-year-old nation with no international standing, nor any international credit before his advent.
However, Madison did, inadvertently I presume, stick America with that insufferable mediocrity Monroe -- so perhaps he shouldn't move TOO far up the list (g!).
While the Lewis and Clarke expedition may have taken place sooner or later, you never know about how timing might have delayed this or that event, perhaps delaying by 20-30 years what we will both agree is the inevitable. History does seem to lurch forward regardless, but there are decisions that propell it rather as opposed to history dragging its participants along if you will. His simple commission of the expedition paid huge dividends and helped significantly to propell the nation West.
The abolition of the slave trade also set him apart, but I do confess that I do not know the subtleties of the politics surrounding that act.
Your information about Madison is good stuff, and perhaps he does not get the credit he deserves. Thanks for such interesting posts.