The effects of a recent government action already are fading. It was obvious when Tokyo and Washington intervened to stabilize the yen that it wouldn’t stick. The Japanese currency has commenced a new downward march, so perhaps it’s time for a new plan.

That joint intervention, in which the Bank of Japan and U.S. Treasury bought yen worth tens of billions of dollars, arrested a slide from about ¥164 per dollar (a 40-year low) to about ¥156. As of Monday it has dropped toward ¥160. The big monetary guns appear to be deterring currency speculators.

But absent fundamental policy changes in Japan, no intervention will prop up the yen indefinitely.