The monthslong Choi Soon-sil scandal and subsequent parliamentary impeachment of President Park Geun-hye are costing the nation a lot. Foreign policy is one of the areas that suffers most dearly.

Park missed the Asia-Pacific Economic Cooperation summit held in Peru in November, sending instead Prime Minister Hwang Kyo-ahn. She was the first South Korean leader to have skipped the annual forum since its launch in 1993.

The 21-member APEC forum usually offers a stage for vigorous summit diplomacy, which past South Korean presidents utilized to enhance cooperation on regional and bilateral issues -- like North Korea’s nuclear threat -- with leaders in the region. In view of the international sanctions being imposed on Pyongyang, such diplomatic initiatives were needed more than ever.

South Korea also lost a key tool to cope with the nuclear and missile threats posed by North Korea -- the trilateral summit talks with Japanese and Chinese leaders. The talks, which had been slated for this month, have been canceled due to the incapacitation of Park. 

The forthcoming change of government in the US is another issue that makes one believe the crisis in the South Korean government could not come at a worse time.

Even in normal times, the inauguration of a new leader in Washington would pose a tough challenge to a South Korean president. This time, a man who many did not expect nor want to be elected is poised to lead the country whose policies affect this and other parts of the world. 

And this nation should take on the new US leader with its president confined to her residence and unable to perform duties as the diplomat-in-chief. This is indeed worrisome, if one recalls what President-elect Donald Trump said about American policy vis-a-vis Korea.

During his campaign, Trump did not hide his negative stance on South Korea, contending, among other things, that the Korea-US free trade pact should be renegotiated, as it is killing American jobs, and that Seoul should shoulder a larger share of the cost for stationing the 28,000 American troops here.

South Korean policymakers will also have to brace for unpredictability in the Trump administration’s policy toward North Korea. Trump called North Korean leader Kim Jong-un a “lunatic,” but later said he was ready to meet with him over a “hamburger.”

In fact, some experts say that Trump go to either extreme in dealing with the North’s nuclear and missile threats -- military action or surprise detente. What is almost certain is that Seoul may not be consulted as closely as during past US administrations.

Trump’s hard-line stance on China also poses a stiff challenge to South Korea. Trump had already taken issue with China regarding trade, climate change and territorial disputes with Southeast Asian countries. He has also publicly challenged Washington’s “one-China policy.”

Moreover, Trump nominated Exxon Mobil CEO Rex W. Tillerson -- a man widely known as a pro-Russia and pro-Putin figure -- as the secretary of state, which also heralds warming US relations with Moscow at the expense of ties with Beijing. 

With so many of our national interests tied to the US and China, conflicts between the two superpowers could affect our security and economy. The Sino-US confrontation over the deployment of a US advanced missile shield system in South Korea is one case in point.

All in all, South Korea is facing the most formidable foreign policy challenges in years, the most serious to come from the likelihood that US foreign policy under Trump will be different and, more importantly, unpredictable.

It is almost certain the current political crisis will go on for at least several more months, while the domestic political situation will not allow acting President Hwang Kyo-ahn to tackle foreign policy issues in earnest. Even if Park is reinstated by the Constitutional Court, she would remain a feeble lame duck.

This calls on Foreign Minister Yun Byung-se to take a more proactive role in the foreign policy arena. For instance, he could have proposed to hold foreign ministers’ talks with his Chinese and Japanese counterparts in lieu of the canceled trilateral summit.

Yun should regard himself as the acting diplomat-in-chief until the next president is sworn in.