Nearly two decades ago, Fareed Zakaria, the international affairs columnist, published a best-selling book called “The Post-American World,” which predicted the United States’ relative decline versus other economically ascendant countries, what he called the “rise of the rest.” (Senator Barack Obama was seen carrying the book around during his first presidential campaign, affirming the volume’s elite sway.) The United States would remain militarily and economically pre-eminent, Zakaria argued, but it could take on a new political role, a sort of chairman of the board for the planet, relying on “consultation, cooperation and even compromise.”