Russian Foreign Minister Sergei Lavrov suggested Tuesday that countries facing sanctions like Iran, Turkey and Russia may start doing business in their national currencies, suggesting that the days of the U.S. dollar as the international reserve currency may be numbered. Perhaps no one would be happier about that than President Donald Trump. Here’s why: As Yale economist Robert Tiffin explained in the 1950s, if a country’s currency is the international reserve currency, then it has no choice but to run a current account deficit. If a replacement is found, as the dollar replaced the British pound in the 1920s, it...