Story highlights Jeffrey Hornung: Japan, South Korea were shaken by statements Donald Trump made while campaigning

Washington's alliances with Seoul and Tokyo will be critical in managing challenges posed by China and North Korea, he says

Jeffrey Hornung is the fellow for the Security and Foreign Affairs Program at Sasakawa USA, a US nonprofit institution providing research and analysis of the US-Japan relationship. The views expressed are his own.

(CNN) The cavalry is coming! Not exactly, but the sentiment of reassurance is the same. This week, US Defense Secretary James Mattis arrives in Asia to visit South Korea and Japan. Two stalwart US allies, policymakers in both capitals have nevertheless been shaken by statements Donald Trump made while campaigning for President. None of these was more dramatic than the suggestion that these allies should pay more for US troops or risk having these forces withdrawn.

Statements like this played to the worst fears in Seoul and Tokyo that the United States might no longer be a committed ally. It is now Mattis' job to reassure them of US commitments and return the trajectory of alliance relations back to pre-2016 presidential campaign rhetoric.

Jeffrey Hornung

Of course, the Trump administration is still less than two weeks old, and specific policies pertaining to the Asia-Pacific security realm are nonexistent. But Seoul and Tokyo are understandably anxious because the closest thing they have to gauge the White House's intentions are memories of what was said on the campaign trail. Indeed, even statements such as presumptive Secretary of State Rex Tillerson's suggestion that he would consider blocking Chinese access to the artificial islands in the South China Sea, and President Trump's vow that he will not allow North Korea to develop missiles that are capable of striking the United States, raise more questions than answers.

It is therefore up to Mattis to bring a message of reassurance to reaffirm US commitment to the alliances and to US engagement in the region. And he is arguably the best placed to deliver this message, not only because of his illustrious military career, but because at his confirmation hearing he spoke to the two issues troubling South Korea and Japan the most when he stressed the importance of alliances and the importance of the Pacific theater.

The decision for Mattis' first official travel to target South Korea and Japan reinforces both the notion that the United States prioritizes the Asia-Pacific region and that it considers the security ties it maintains with South Korea and Japan to be important. Meanwhile, reaffirming the importance of robust alliance relationships signals that, despite all the campaign rhetoric by candidate Trump, these crucial alliance relationships might not deviate all that far from the relations we have known heretofore.

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