Taiwan's main opposition Democratic Progressive Party, DPP, Chairperson Tsai Ing-wen speaks during a press conference in Taipei, Taiwan, April 15, 2015. [Photo/IC]

Close attention will be paid to Taiwan leader Tsai Ing-wen's transit via the United States when she travels to Guatemala in early January, for it will shed light on what direction Sino-US relations will take when Donald Trump enters the White House.

Despite Beijing's opposition, the US insists it is a "long-standing practice" since it has given the nod to such transits by leaders of the island many times before.

However, Tsai's transit is taking place soon after she and Trump held a phone conversation, breaking with decades of precedent.

No incumbent or incoming US president has spoken by phone with a Taiwan leader since 1979, when Beijing and Washington established diplomatic relations.

The incident, if indeed by design as reported, could indicate a major US policy shift that would threaten relations, since they are built on the long-standing acknowledgment by the US of one China, which is the sine qua non for healthy relations.

So far Beijing's response to the conversation has remained restrained. It has taken a wait-and-see attitude, giving Trump the benefit of the doubt since he is a novice in foreign policy and won't take the helm until the Jan 20 inauguration. Beijing has demonstrated calmness and confidence again after Trump, in a twitter tirade, lambasted China for its trade, currency and South China Sea policies on Sunday; and even after his economic adviser Stephen Moore went so far as to say "screw them" in a vulgar verbal attack against China.

Such prudence is laudable for the time being, for a good Sino-US relationship serves not only the best interests of people in both countries, but also peace and stability in the Asia-Pacific and beyond.

However, with separatist-minded Tsai due to set foot on US soil, further provocative moves by the US president-elect and his team cannot be ruled out given the reckless and impulsive style of leadership that Trump displays. Especially, as hawks in the US have never given up hope of using Taiwan as part of the US' pivot to Asia aimed at containing the mainland's rise.

Although Beijing has shown that it is willing to keep the bigger picture in mind, this attitude should not be mistaken for weakness.

China has to prepare for the worst, even though it will continue to do all it can to maintain a healthy bilateral relationship. What has happened over the past weeks tends to suggest that Sino-US relations are facing uncertainty as never before, as Trump's words are not necessarily more bark than bite.