Dear America, why did you let us down?

The election of Mr. Trump feels like a sudden plunge after a gradual decline. Already he is goading China, befriending President Vladimir V. Putin, disregarding climate change and refusing daily intelligence briefings because he’s “a smart person.” None of this, we fear, will end well for any of us.

And here we Australians are on the edge of Asia, a small and loyal ally of the United States, with a significant and growing Asian-born population, caught between our strategic alliance with you and our economic future with China. Britain is tangled in Brexit, with neither the time nor the inclination to focus on a former colony on the other side of the world. We feel worried, lucky — and alone.

Earlier this year, Australia’s Department of Defense outlined the long-term outlook for our defense and security, emphasizing that the relationship between the United States and China will continue to be the most strategically important factor in the region. “The governments of both countries have publicly committed to a constructive relationship and it is not in the interests of either country to see an unstable international environment in which the free and open movement of trade and investment is compromised,” the department noted. That constructive relationship must now be spoken about in the past tense.

And no longer can it be assumed that Australia will always pick the United States over China, if forced to choose.