Biden bids for activist world role. Will Americans back him?

“America is back.” President-elect Joe Biden’s message to the world has been clear, to friend and foe alike. That could prove easier said than done, though, and one early challenge awaiting the next U.S. administration will serve as a signal.

Unsurprisingly, it is pandemic-related: What will Washington do to distribute promising U.S. and European vaccines in developing countries, amid concerted drives by two strategic rivals, China and Russia, to promote vaccines of their own as part of a broader effort to extend their political and economic influence?

Mr. Biden has...