New Delhi, March 8 -- Last night US President Donald Trump announced - unilaterally - that India has agreed to take its tariffs "way down". For those of us who had hoped reality would somehow turn out more sober than Trump's rhetoric suggests, his shock decisions have been a rude awakening. The Trump Trade War officially started this week. (While tariffs on most goods from Canada and Mexico are now paused until 2 April at least, the reprieve could well be temporary.)

Do tariffs work, and what is Trump trying to do? It's not advisable to try and second-guess such an unpredictable man, but his role model also presided over a high-tariff regime designed to protect domestic American industries.

In his inaugural address, Trump harked back to...