WASHINGTON North Korea's next act of defiance could be a critical test of whether President Barack Obama's "strategic patience," his long-standing policy toward the nuclear renegade state, is beginning to run out.
With North Korea considered likely to cap its barrage of bellicose threats with a military provocation in coming days, the United States has drawn up new security plans with ally South Korea and increased pressure on China to do more to rein in Pyongyang, U.S. officials said.
The recalibration of Obama's approach to North Korea includes revised rules of engagement to respond to any attack more forcefully than in the past, but in a way that avoids a spiral into all-out war, the officials said.
Even so, the question is whether the broader diplomatic policy that Obama's aides have dubbed "strategic patience" - which seeks to isolate North Korea and not offer diplomatic rewards for its provocations - can meet the challenge of what has become one of the most serious crises on the peninsula since the end of the Korean War in 1953.
So far, the Obama administration has failed to stop North Korea's nuclear advance. Since Obama became president, Pyongyang has conducted two underground nuclear explosions and several banned missile tests.
Obama's predecessors didn't have much success reining in North Korea's weapons programs, either. But Obama faces a higher degree of uncertainty thanks to North Korea's young leader, Kim Jong-un, who issued a stream of hair-raising threats in response to U.N. sanctions and joint U.S.-South Korean military drills.
"There are plenty of miscalculations that are possible," a senior Obama administration acknowledged. "We are calibrating our approach and our strategy to Kim Jong-un's behavior."
'GRAND FINALE WITH FIREWORKS'
If Kim sticks to the North Korean playbook, as U.S. policymakers predict, Pyongyang will test-fire one or even two missiles around April 15, the birthday of the country's founder, Kim Il-Sung, Kim Jong-un's late grandfather.
"A grand finale with fireworks to end the arc of escalation ... is certainly plausible," the senior official, who spoke on condition of anonymity, told Reuters.
U.S. and South Korean forces would do nothing if, as they expect, the missile heads for open water. But they would be ready to shoot it down if it threatens South Korea, Japan or the U.S. territory of Guam, another administration official said.
U.S. officials have not ruled out the possibility, however, that North Korea could instead carry out a strike on a South Korean ship or border post. This would trigger "proportional retaliation" by South Korea, though precautions have been put in place in hopes of avoiding escalation into open conflict, they said.
The new security arrangement, first reported by the New York Times on Monday, is meant to reassure South Korea - which restrained itself after being caught off guard by a pair of North Korean attacks in 2010 - that it would have room to respond militarily to any new provocation.
But there are risks. "Such a stance puts the peninsula on an unpredictable hair trigger," wrote James Schoff, an Asia expert at the Carnegie Endowment for International Peace.
The United States also wants China - the closest thing North Korea has to an ally - to go beyond just rebuking Pyongyang and fully implement the U.N. sanctions that it recently negotiated with Washington.
U.S. officials recognize there are limits to how much China is willing to tighten the screws on North Korea, fearing that if its troublesome but impoverished neighbor collapses the resulting flood of refugees could be disastrous for Beijing.
But the U.S. show of force on and near the Korean peninsula is a message to China that its failure to crack down on Pyongyang could mean a larger American military presence in the region, something Beijing opposes.
Even as tensions rise and the Obama administration adjusts accordingly, it is showing no signs of abandoning its "strategic patience" approach altogether.
"What's important is we not allow North Korea to profit one iota from this situation," the senior official said.
Calls for naming a high-profile U.S. envoy have little support in the White House.
And Obama himself has refrained from responding personally to North Korea's threats, a strategy aimed at depriving Kim Jong-un of presidential attention.
Obama's predecessor, President George W. Bush, veered from a tough policy toward North Korea in his first term to concessions aimed at boosting diplomacy in his second. He took North Korea off the U.S. list of terrorist-sponsoring nations and unfroze bank accounts controlled by the Kim family.
Obama took office in 2009 promising more engagement with North Korea as he offered to extend a hand to America's foes who were "willing to unclench your fist." Four months later, North Korea launched a missile in violation of U.N. resolutions, sending the relationship back off the rails.
The policy of "strategic patience" took hold, essentially launching a diplomatic waiting game in which Washington focused on sanctions and condemnation while leaving the door open to easing North Korea's isolation if it behaved better.
Pyongyang went on to scrap international talks and conduct a second nuclear test. In 2010 it was blamed for the sinking of a South Korean warship, and then shelled a South Korean island.
The last hint of a thaw came in February 2012, just months after Kim Jong-un came to power, when Obama offered food aid for a moratorium on nuclear and long-range missile tests.
But the deal imploded within weeks when Pyongyang announced plans for what it called a satellite launch and U.S. officials said was a ballistic missile test.
Even as successive administrations have made the issue a priority, the North is believed to have accumulated enough plutonium for about half a dozen bombs, though it is still years away from developing a nuclear warhead, according to experts.
The non-partisan Congressional Research Service concluded in February that Obama's strategic patience was essentially aimed at "containing North Korea's proliferation activities rather than rolling back its nuclear program."
"Underlying the approach is an expectation that North Korea will almost certainly not relinquish its nuclear capabilities," it said in a report. But the policy, the report noted, also allows North Korea to control the agenda, referring to how Pyongyang manipulates the United States and its allies to react to North Korea's actions.
But in a sign of just how thorny a problem North Korea has become, even Obama's Republican opponents seem at a loss for a better solution. Normally a tough critic of the Democratic president, U.S. Senator Lindsey Graham told NBC's "Meet the Press" program: "I appreciate what this administration is doing."
(Reporting by Matt Spetalnick and Anna Yukhananov; Additional reporting by Phil Stewart; Editing by Warren Strobel, Mary Milliken and Eric Beech)