“In carrying out their first joint effort in a generation to boost the yen, the U.S. and Japan are seeking to contain tremors that could be triggered by a cratering Japanese currency,” the Wall Street Journal reports.“The yen’s slide to a 40-year low indirectly threatened to bump up U.S. interest rates and risked throwing a wrench in plans to pull billions of dollars of Japanese investment into the U.S. ““By propping up first Argentina’s currency and now the yen, President Trump is showing that he’s prepared to help allies who are battling financial markets, a contrast to the hands-off approach long favored by U.S. policymakers except in moments of exceptional peril.”