Nothing’s happened yet but something big could happen soon, so let’s get a post up to make sure we’re all on the same page. Remember in March when that South Korean ship exploded, killing 46 sailors on board? It was no mystery who did it, but not until this past week did U.S. intelligence conclude that the orders to sink it came straight from the top.

The officials said they were increasingly convinced that Mr. Kim ordered the sinking of the ship, the Cheonan, to help secure the succession of his youngest son.

“We can’t say it is established fact,” said one senior American official who was involved in the highly classified assessment, based on information collected by many of the country’s 16 intelligence agencies. “But there is very little doubt, based on what we know about the current state of the North Korean leadership and the military.”…

Under the leading theory of the American intelligence agencies, Mr. Kim ordered the attack to re-establish both his control and his credentials after a debilitating stroke two years ago, and by extension reinforcing his right to name his son Kim Jong-un as his successor…

Victor Cha, a North Korea expert at the Center for Strategic and International Studies in Washington and a former official in the National Security Council during President George W. Bush’s second term in office, noted that when Mr. Kim was on the rise three decades ago, “there were similar incidents designed to build his credibility” as a leader.

They leaked the analysis over the weekend because Hillary and a bunch of other cabinet officials are in China today and of course will use the report to pressure Beijing to rein Kim in before he does something so nutty that South Korea has no choice but to respond. The first step is a Security Council condemnation, which China will be asked to join. The next step? Well, according to South Korea’s president, they’re changing their military posture from “passive defense” to … “proactive deterrence.” Via Business Insider, gird your loins:

“If our territorial waters, airspace or territory are militarily violated, we will immediately exercise our right of self-defense,” Lee said in an address to the nation, televised live Monday morning.

“From this moment, no North Korean ship will be allowed to make passage through any of the shipping lanes in the waters under our control, which has been allowed by the Inter-Korean Agreement on Maritime Transportation,” Lee said. “The sea routes meant for inter-Korean exchanges and cooperation must never again be used for armed provocations.”…

“Trade and exchanges between the Republic of Korea and North Korea will also be suspended,” Lee said.

“However, we will continue to provide assistance for infants and children,” he said. “Matters pertaining to the Kaesong Industrial Complex will be duly considered, taking its unique characteristics into consideration.”

They’re also promising to install loudspeakers at the border to blast anti-Kim propaganda, a tactic they’re used in the past; North Korea says if they do it, they’ll open fire. I’m not too worried yet, as the fact that SK is promising to continue humanitarian aid at least creates some space for de-escalation, but offhand I can’t recall a moment in recent years where the cold peace on the peninsula has been this fragile. Somewhat to my surprise, not only is Obama offering “unequivocal” support for South Korea’s defense, he’s rattling the saber by ordering U.S. commanders in Korea to “ensure readiness” and authorizing joint naval exercises with SK in the “near future.” The calculus, of course, is that a show of force will concentrate Kim’s mind on the price of further escalation, which … is not what would I have expected from Hopenchange circa 2008. Circa 2009, though? Hmmmm.

If, god forbid, this thing does escalate further, it’ll be an explosive test of where the left and right now stand vis-a-vis America as guarantor of its allies’ security. The U.S. military presence in Seoul is tolerated back here because it’s a low-cost way of deterring a very high-cost confrontation, but if deterrence finally breaks down and this thing turns hot, how will the public cope with American casualties? Will Democrats stand behind The One? Will the isolationist/Paul wing on the right push the GOP into opposing him?