Just because the US changes political direction, that doesn't equate to instability. Its aims are changing, like it or not, good or bad. The US deciding it wants Greenland is not a proof of instability, it's a change in the strategic goals held by the people controlling the superpower.
And the US is at a high level of strength, not weakness. Its large corporations hold sway over the globe in a manner the likes of which has never been seen before in modern history. Its military has force projection to nearly every point on the globe, with hundreds of global military bases. Its national wealth is at an all-time high. Its stock markets are at all-time highs. Its median income is at an all-time high. Its median disposable income is at an all-time high. Its housing wealth is at an all-time high.