Earlier quoted context omitted.
He was elected, despite his numerous faults - so he and his policies are emblematic of at least enough of the country to be politically relevant.
What does "political relevance" have to do with political longevity? We're not a fundamentally different country now than we were last year, and policies created with a pen stroker can be struck down just as easily. Anyone who thinks that Trump's policies are a good predictor of future US policy need to explain their rationale because it doesn't follow reason.
Thus, no matter how progressive or good-neighborly future administration policies are, allies now have to build in the risk that every 4 years there will be a 50:50 chance that those policies will be reversed and any agreements voided.