‘America is back.’ What that means to the world.

“Welcome back America!”

The celebratory tweet from Paris Mayor Anne Hidalgo came just minutes after the U.S. television networks had called the presidential election in favor of Joe Biden last weekend, and her response has been echoed in the days since by many U.S. allies around the globe.

The underlying message: In an increasingly fractious world there is a strong desire to feel America’s presence. Especially in the face of borderless challenges like the COVID-19 pandemic and climate change, hopes are high that the most powerful democracy on earth will...