New Delhi, March 28 -- Suddenly, the R-word has staged a comeback. As US President Donald Trump's on-again-off-again tariff war holds the world in thrall, some economists (admittedly, a minority so far) worry that the world's largest economy could be headed for a recession. This is a possibility that, ironically, even Trump has refused to rule out, opting instead to say the US must be prepared for a period of pain as part of a "transition."

This admission is puzzling, since there is little that leaders, especially in democracies, abhor more than presiding over a recession. The prospect, however remote, opens up a host of questions. Apart, of course, from the tricky question of how and when one should call a recession.

Economists may be ...