U.S. President Donald Trump's foreign policy, such as it is, rests on a massive and apparently indestructible contradiction. Trump wants the United States to remain the "essential" nation, the best embodiment of Western ideals of freedom and democracy, while at the same time deliberately alienating many of our traditional "allies," whose support the U.S. desperately needs. American leadership becomes difficult, if not impossible.

It is hard to straddle this contradiction, because it reflects a basic misunderstanding of the American "greatness" that Trump so avidly pursues. To Trump, this greatness is mainly measured in economic terms: the number of added jobs; the trajectory of wages; the rate of economic growth. It is a nostalgic and unrealistic yearning for the economic dominance the U.S. enjoyed in the 1950s and 1960s.

The truth is that American greatness then and later was never about dollars and cents alone. Prosperity was a means to an end, not an end in itself. The greater objective was to promote democracy and mixed economies, with power divided between the market and government. To advance this vision, the U.S. advocated open trade and provided a military umbrella. The latter created a geopolitical shield against instability.