The sinking of the patrol ship Cheonan on March 26 has put the South Korean government in a serious bind at a most inopportune time.

With local elections looming, the last thing President Lee Myung-bak wanted was an international crisis that magnified defense shortcomings and distracted voters — and investors — from South Korea’s relatively impressive GDP growth over the last two quarters.

Tragically for the 46 sailors who lost their lives aboard the Cheonan, Fortuna — and allegedly North Korea — did not care what the South Korean leader preferred.

President Lee is now faced with the difficult decision of responding in a manner that satisfies the country’s national security needs without upsetting its economic recovery or its standings at the polls. And it definitely should be Seoul’s call — not Washington’s.

So how should President Lee respond?

Thus far, the evidence has not conclusively demonstrated North Korean responsibility for the destruction of the Cheonan. Nevertheless, the preponderance of data suggests that a North Korean torpedo sank the ship.

Seoul must demonstrate North Korean fault to the satisfaction of the South Korean people and the international community before proceeding with any other action. That the government has taken great care in assessing responsibility thus far shows that it understands this point.

If the evidence ultimately confirms that North Korea sank the Cheonan, President Lee needs to find a Goldilocks solution to the crisis.

He must craft a policy that is neither so aggressive as to provoke a spiral into general war with all of its associated human and economic costs, nor so meek that North Korea is emboldened, the demands of justice for the dead and wounded sailors unmet, and the public’s security concerns undiminished.

Lee needs to send an appropriate message that answers the North Korean challenge. However, this is not merely a two party conversation.

The situation is complicated by the fact that South Korea must send messages to at least three different audiences — and they must be clear enough to be properly understood.

To the people of South Korea, the government must show that the armed forces are capable of responding to North Korean aggression.

It must tell them it will not allow their sons to be killed with impunity even if that comes at a cost in blood and treasure. To the international community, Seoul must craft a careful, measured response indicating its understanding of the delicacy of the regional situation and portraying itself as the responsible party.

The message sent to the North Korean government must be that aggression will result in painful consequences so that in the future Pyongyang will not believe that it can act with impunity.

Unfortunately, we are not confident that any of the approaches currently under discussion meets the Goldilocks test and sends the appropriate messages.

Taking the issue to the U.N. Security Council is a proper first step, but is unlikely to solve the problem. As Stephan Haggard of UC-San Diego argued, there is not really “anything that the five Security Council members can sign on to other than what they have been already doing.”

This leaves South Korea in the position of having to respond on its own. And the softer approaches under consideration such as cutting off some trade, banning North Korean ships from the Jeju Strait, or restarting information operations in the DMZ seem much too little to allay popular concerns at home or deter future aggression from the North.

It may be that some military pinprick is warranted. But accomplishing such a task without provoking a wider engagement will require careful target selection and firm but measured diplomatic talk.

Indeed, North Korea might welcome a military provocation in order to distract its people from the dreadful economy and repressive political situation.

There is no question that the next few weeks will present President Lee with an extraordinarily challenging set of problems.

But if he can thread the needle, his handling of the crisis will be hailed as a signature foreign policy victory. Failure likely means greater cost in the future — which is why the mantle of responsibility is a heavy one.