My thanks and ours at AC to Jonathan Rowe for posting it. It's one of the best pieces I've ever read on the prevailing sentiments around the time of the Founding. I got a sense of the zeitgeist, the spirit of the times---what it felt like to be an American in those times with all those ideas flying around, so much more than the recent history/anthropology pieces whose focus is too narrowed onto a particular group or way of thinking.
"Liberalism" as used in the Founding era isn't quite what we think of today, not "progressive" or governmental or social programs in that FDR or LBJ way, so let's clear the decks of the partisanship thing first and foremost.
Hamburger also poses a serious challenge not only to the Whig Theory "republicanism" narrative of eminent historians Bernard Bailyn and Gordon Wood, and to their critics as well, the new generation of historians who do the race/class/gender thing.
So let's let the man speak for himself. A partial summary, and some thoughts:
Basically, young America's enthusiasm for "liberalism" was more an enthusiasm for the freedom from the old ways of Europe, both in its rigid aristocratic class system and the religious orthodoxy of the "established" Christianities, Roman Catholicism to be sure but also the Church of England [Anglicanism].
And for free trade! As we know from Adam Smith, commerce and the government [then and now] get a bit too cozy and corrupt, another encumbrance from the Old World to be shed. Nations that trade together stay together.
This "liberal" vision reminds me of nothing so much, as Francis Fukayama's "The End of History," where the world lives in peace under political, religious, and economic liberty, Western-style bourgeois liberal democracy.
Hamburger sharply notes that even GWashington falls victim to this rosy view of "historicism," that it was the old encumbrances and illiberalities of the Old World that brought about war itself, and may someday become unnecessary.
The fly in the ointment---the intruding reality---is man's nature, which is not rosy. "Eliphaz Liberalissimus" is the pseudonym of Rev. Ashbel Green, and his Important Matters, a Liberal Man's Confession of Faith  is a devastating satire of the mind that's so liberal it abandons not only all tradition and belief, but common sense as well. "Liberty" indeed becomes license, and Green's satire is spot-on and prophetic about the mushy "liberalism" if not hedonism of our own age, where anything goes.
Except belief or principles, of course. Those things are "illiberal," eh?
There are limits to the wonderfulness of human nature. One of GWash's 1786 letters to John Jay, who'd become his confidant, puts it this way:
"Your sentiments, that our affairs are drawing rapidly to a crisis, accord with my own. What the event will be is also beyond the reach of my foresight. We have errors to correct. We have probably had too good an opinion of human nature in forming our confederation. Experience has taught us, that men will not adopt & carry into execution, measures the best calculated for their own good without the intervention of a coercive power. I do not conceive we can exist long as a nation, without having lodged somewhere a power which will pervade the whole Union in as energetic a manner, as the authority of the different state governments extend over the several States. To be fearful of vesting Congress, constituted as that body is, with ample authorities for national purposes, appears to me the very climax of popular absurdity and madness.
We must take human nature as we find it. Perfection falls not to the share of mortals. "
James Madison pops up now and then in Hamburger's essay: Fortunately for us and the new American republic, James Madison was quite the realist about man's darker side, and didn't fall into the rose-colored glasses "liberalism" that was all the buzz. And so he helped design the Constitution in 1787 with the "separation of powers" we still hold onto somewhat today, trusting the human beings in the new national government no more than the Articles of Confederation government of 1786.
Me, I think it's James Madison's non-rosy view of human nature that got our American republic into the record books of man's history. The American Constitution was ratified June 21, 1788. 222 years and counting...
Hamburger's essay brings one last thought to the fore: If you want to see where the "rosy" view of human nature and "republicanism" lead, just look to the French Revolution. The perfect republic will only come about when there are perfect men to rule it and populate it as citizens.
James Madison knew better:
"If men were angels, no government would be necessary."
The "liberalism" of the French Revolution was that the French were dumping their Old Order, the ancien régime of aristocracy, clericalism, and monarchy.
And they said, screw it. All bets are off. And we know how that turned out.
The American Revolution also dumped aristocracy, clericalism, and monarchy in favor of liberalism. The difference from the French version was that the American Founders weren't just forming a new government, they were forming a new nation not only to "secure the Blessings of Liberty to ourselves," but to "our Posterity."
All bets were on, and there you have it.