Canadian Politics Today

I don't know if its quite as fluid as you are making it out to be.

For example, some trade deals (e.g. NAFTA) have ~25 years (through both Democratic and republican administrations). NATO hasn't really changed much. It kept its isolationist policies against Cuba for decades. It still abides by various arms control treaties (such as various nuclear test ban agreements). And the US still follows the Munroe doctrine.

Granted, Trump has been an absolute wrecking ball (pulling out of NAFTA,TPP and the Paris accords), harming America's standing in the world and showing itself to be completely untrustworthy. But he seems to be the exception. Usually most presidents don't made radical changes because they are either willing to stick with what works, or if they make changes will do so slowly over time.

The things that we are consistent on are still there because they continue to suit us (or we assume they still suit us).