Currency intervention is a form of theatre. It rarely changes the fundamentals

CURRENCY intervention is a form of theatre. It looks decisive. It rarely changes fundamentals.

The latest performance was nonetheless notable. On July 31st Japan and the United States conducted a coordinated operation to buy the yen, the first bilateral intervention of its kind since the G7 acted after the 2011 earthquake and tsunami. The yen had been sliding relentlessly, reaching 163.73 against the dollar on Thursday of that week, its weakest level in roughly four decades. Within days of the joint move it had recovered to the high 150s. Both governments vowed they "will not hesitate" to act again. Former Bank of Japan policymaker Sayuri Shirai... warned in June that the yen could weaken further to 165 if the Federal Reserve raises interest rates. Her view is that markets will test the floor again, and that the floor is made of words.

She is right to be sceptical. The question is not whether authorities will intervene again. It is whether anything they do can alter the arithmetic that pushed the yen to the brink in the first place.

That arithmetic is a rate differential. The Fed's policy rate sits at 3.5%-3.75%, a position it held at its July 29th meeting in a divided 9-3 vote, with three members wanting a quarter-point hike. Markets now price roughly a 60% chance of such a hike in September. The BOJ's policy rate, by contrast, stands at 1%, the highest since 1995 but still more than two percentage points below the Fed's. Capital flows to higher yields. When the gap is that wide and persistent, speculative short positions in the yen swell to levels last seen in mid-2024. Buying yen with foreign-exchange reserves can dent the price temporarily. It cannot close the gap.

The deeper problem is that the gap is not an accident. It is the product of two governments whose domestic politics make the obvious solution politically painful. The BOJ has moved at a glacial pace because raising rates further risks destabilising Japanese government bond markets and, more importantly, increasing the cost of servicing Japan's enormous public debt. Prime Minister Sanae Takaichi's administration compounds the dilemma. In July she announced plans to cut the consumption tax on food from 8% to 1% for two years, starting in April 2027, along with broad fiscal stimulus. The consumption tax is the first to be cut since its introduction in 1989. Expansionary fiscal policy, combined with inflationary pressure from a weak currency and energy costs, is exactly the mix that pushes a currency down. Ms Takaichi has a political incentive to spend. The BOJ has an institutional incentive to move slowly. Neither actor can easily change course without the other yielding first.

Washington's participation adds a new wrinkle. The U.S. Treasury's involvement is often described, by President Donald Trump, as a "signal of friendship." That is part of it. But the self-interest is more revealing. Japan is the largest foreign holder of U.S. government debt. Unilateral Japanese intervention would require selling Treasuries, potentially flooding the market at a time when the 10-year U.S. yield has risen almost 57 basis points this year. Louise Loo of Oxford Economics called it a "self-preservation element": preventing Tokyo from destabilising U.S. funding markets in desperation. The Treasury made the accommodation explicit by announcing that Japan can use the Federal Reserve's FIMA repo facility, which allows foreign central banks to borrow dollars against Treasury collateral without selling outright. That is generous. It is also a recognition that the United States has more to lose from a Japanese fiscal scramble than from a weaker yen.

There is an odd detail worth noticing. Reports indicate the U.S. sold euros, not dollars, to buy yen in the intervention. Robin Brooks of the Brookings Institution pointed out that this twists the traditional mechanics of coordinated intervention, which normally involves dollar assets. Selling euros suggests the U.S. was trying to spare Japan - and its own Treasury markets - from a bigger dollar outflow. It signals a desire to look cooperative while limiting the actual commitment. In FX markets, where credibility matters more than volume, the twist may undermine the very efficacy it was meant to protect. If investors conclude that Washington's participation is more about optics than substance, the deterrent effect fades.

To be sure, intervention is not useless. The coordinated announcement did prompt an immediate and visible rebound, with the dollar falling sharply against the yen in the days that followed. Ms Shirai herself acknowledged that the yen could reach 165, not that it must. And the BOJ's July meeting, which held rates steady at 1%, carried the most explicit forward guidance yet that further hikes are coming. Markets now expect a move to 1.25% by year-end. Even a modest tightening cycle, combined with the credibility of a U.S. safety net, could keep the yen from collapsing to 165 or beyond.

Yet the structural direction has not changed. The Fed faces persistent inflationary pressure - the July FOMC statement noted that inflation "remains elevated relative to the 2% goal, in part reflecting supply shocks" including energy - and a hawkish minority on the committee that could push rates higher. Japan's fiscal trajectory, for all Ms Takaichi's intentions to help households, points toward more debt, more inflation, and, absent a corresponding monetary tightening, more pressure on the yen. Stephen Innes of SPI Asset Management summarised it tersely: the yield differential remains wide, Japan's energy-import burden remains significant, and the BOJ is still moving more slowly than markets require for a sustained reversal.

The real test is not whether Japan and the U.S. will intervene again. They almost certainly will, if the yen resumes its slide. The test is whether the BOJ will raise rates fast enough to make interventions redundant. That requires the central bank to resist pressure from an administration that needs cheap money to fund expansionary plans. It is a familiar political trap: governments that weaken their currency with fiscal policy often punish the central bankers who would fix it.

Currency crises rarely arrive as sudden collapses. They accumulate through a series of small decisions that each look defensible in isolation. Ms Takaichi's tax cut. The BOJ's cautious pace. The Treasury's euro-funded intervention. Taken together, they defer the reckoning without resolving it. A stronger yen requires a higher Japanese rate, or a lower American one, or both. Neither government appears willing to make the move that would deliver it.

The yen may not break. But the bargain that holds it together - fiscal indulgence subsidised by monetary restraint and diplomatic theatre - is a fragile one. When the next shock comes, intervention will not be enough.