From yesterday's editorial in the Philadelphia Inquirer about the conviction of a local political boss, Vince Fumo, on 137 corruption-related charges:
There was an unindicted co-conspirator in the case against Fumo. That would be the city that spawned him, took what he delivered and then pretended to be shocked, shocked at the unsavory details of how he manipulated the process.
That, of course, would be Philadelphia. That, of course, would be us.
The editorial's headline is "We've met the enemy, and he is us".
Linguistically speaking, this all started in 1813, when Commodore Oliver Hazard Perry famously wrote to General William Henry Harrison reporting a victory in the Battle of Lake Erie:
We have met the enemy and they are ours. Two ships, two brigs, one schooner and one sloop.
The quotation is often amended to "… and he is ours", perhaps due to prescriptive nervousness about "singular they". In particular, when Walt Kelly invented his now-even-more-famous variant, it was in the form
We have met the enemy and he is us.
The Wikipedia entry for Walt Kelly similarly singularizes the original to fit:
Perhaps the most famous quotation … is, "We have met the enemy and he is us" (a paraphrase of Commodore Perry's famous "We have met the enemy and he is ours" from the War of 1812). The earliest form of this expression appeared in his introduction to The Pogo Papers (1953); it was used much later in the comic strip and as the title of a collection of strips.
I'm not sure exactly what the context of the original use in 1953 was, though I think it had something to do with McCarthyism, the message being roughly that some reactions to an external threat can become more dangerous than the threat itself. These days, the best-known cartoon versions of the Pogo catch-phrase are the ones from strips commemorating Earth Day 1970 and 1971 (click on the images for larger versions), where the threat is internal and the response is seen as entirely benign:
There are hundreds of further adaptations of this phrase out there, as a quick web search will show. "We (or sometimes I or You) have met the enemy and he is Y" takes on values of Y = you, me, Republican, Democrats, each other, my stomach, Alabama, the Tax Collector, Crabgrass, gay, awesome, Force Structure, some fat guy in Florida, strange, Wall Street, …
The plural version "… and they are Z" comes in flavors of Z = Partly Right, Armed with Pennies, The Tombstone Militia, Earmarks, illiterate, GUI's, curs, weird, annoying, …
But the Inky's editorial makes a different sort of modification: from "he is us" to "that would be the city that spawned him", before working back to "that, of course, would be Philadelphia" and finally "that, of course, would be us."
The basic reason for this internal modification, I think, is stylistic. It would be confusing to follow "There was an unindicted co-conspirator" with "He is the city that spawned him"; and "They are the city that spawned him" is even worse. Choices like "It is …" or "That is …" are problematic, in part because they lead the reader down the garden path of common constructions with pleonastic it or summative that, like "It is obvious that …" or "That is why …"
So the editorial writer chose the fashionable "that would be …" construction, which is often deployed these days as a way of answering a (real or rhetorical) question, just as in this passage. Adding "of course" to the second two repetitions isolates the repetitions of "that" syntactically, conveying in writing an emphasis that might have been delivered prosodically in speech.
At this point, in the universe of evoked associations, the naval hero and the comic-strip possum meet an urban legend that was discussed last year in a guest post by Larry Horn ("That would be in the modal auxiliary, Bob", 1/9/2008).
[I've ignored several other linguistic allusions in the mere 50 words quoted from this densely intertextual editorial: the "shocked, shocked" reference to Casablanca, and "unindicted co-conspirator", which for many people traces back to Watergate.]