And now, the most-talked-about exchange from last night’s debate.

As conveyed in the transcript:

But I think Governor Romney maybe hasn’t spent enough time looking at how our military works. You — you mentioned the Navy, for example, and that we have fewer ships than we did in 1916. Well, Governor, we also have fewer horses and bayonets — (laughter) — because the nature of our military’s changed. We have these things called aircraft carriers where planes land on them. We have these ships that go underwater, nuclear submarines.

And so the question is not a game of Battleship where we’re counting ships. It’s — it’s what are our capabilities.

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The “horses and bayonets” line was the most-tweeted of the night. Obama’s argument was clear: The needs of the military change and evolve over time. Ships are less necessary now than in 1916 because we have planes, rockets. Problems change, and so do the tools we use to address them.

But just as quickly as Obama made that argument, partisans lined up to defend Romney, arguing in favor of bayonets. Here’s the chair of the Republican National Committee.

Today, Mitt Romney’s running mate took the argument a step further. On CBS This Morning (this morning), Paul Ryan said he “didn’t understand” the president’s remark. And then, something dumber.

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To compare modern American battleships and Navy with bayonets … I just don’t understand that comparison. Look. We have to have a strong Navy to keep peace and prosperity and sea lanes open. The president’s — all these defense cuts, if all these defense cuts go through, our Navy will be smaller than it was before World War I. That’s not acceptable. And, yes — the ocean hasn’t shrunk. You still need to have enough ships to keep our sea lanes open, to keep our strength abroad where it needs to be.

You catch that? “The ocean hasn’t shrunk.”

No, Mr. Ryan, the oceans haven’t shrunk. In fact, quite the opposite is happening. Sea levels are rising and the ocean is expanding. Your home state of Wisconsin may not be too worried about it, but the city where you’ve lived most of your adult life — Washington, D.C. — certainly is.

But then, maybe that’s Ryan’s point. That human-caused warming will expand the volume and surface area of the ocean necessitating a revamped Navy, one capable of diving in deeper seas and patrolling over now-flooded cities. Maybe his argument this morning was the only subtle nod to a changing world that we’ll see during the last two weeks of this campaign, a wink to climate hawks that he’s paying attention and hearing their concerns.

Ha ha. Nope. He just wants to reassure voters in the swing state of Virginia that the government will create jobs in the only way Republicans ever admit it does: writing checks to military contractors.

The president’s argument last night was that the nation’s tools and problems keep changing, that we evolve along with them and should not rely on entrenched answers to brand new questions. But the man he was speaking to, and that man’s running mate, are campaigning on a platform predicated on addressing modern challenges with archaic solutions: social issues, foreign policy, and — most of all — energy. Obama says we need to invest in new military tools and green energy. Romney says we need to build more battleships and burn more oil.

After all, the oceans will remain a constant size, forever.