A foreign treasury secretary should not be a central bank's biggest cheerleader

CENTRAL BANKS derive their authority from the promise that they set policy in the economy's interest, not in the mood of the moment or the preference of a foreign government. That promise is under quiet strain in Japan, where the Bank of Japan finds itself caught between domestic fiscal chaos and unusually overt encouragement from Washington. Scott Bessent, the American treasury secretary, has called Kazuo Ueda a 'longtime friend' and praised the BOJ's 'strong commitment to monetary and financial stability'.

The backdrop is a yen that has fallen to its weakest level in roughly four decades. At its low in late July the currency was quoted at 163.73 per dollar. The slide has been driven by a familiar mix: rising oil prices, Japan's persistent budget deficits and a yawning interest-rate gap. The BOJ lifted its policy rate to 1% in June, its highest level since 1995, but that is still far below the Federal Reserve's 3.75%. Real borrowing costs in Japan remain deeply negative, meaning the hike did little to arrest the yen's decline.

The most recent episode is extraordinary. On July 31st and August 1st Japanese authorities and the United States conducted one of the closest coordinated currency interventions in decades. Japan alone spent around ¥8.45trn ($52.8bn) in a single day on Thursday, likely the biggest single-day intervention in Tokyo's history, according to Bloomberg data compiled from BOJ accounts and money brokers' forecasts. The yen rebounded to the 157 range. Mr Bessent confirmed the operation on Friday, saying it "countered disorderly yen movements", and added that the Treasury "will not hesitate to participate in further joint intervention".

The intervention itself was oddly constructed. The New York Federal Reserve reportedly sold euros, rather than dollars, to buy yen. The twist surprised markets, because coordinated intervention has traditionally been funded with dollar assets. Robin Brooks of the Brookings Institution, a think-tank, suggests the manoeuvre could ultimately weaken rather than strengthen confidence in the yen, because it invites investors to wonder why the United States did not fund the purchase out of dollars, which would have been the stronger signal. If Washington was trying to spare Japan from selling American Treasuries to finance the operation, the gesture may have cost more credibility than it bought.

Yet the intervention is the more visible part of a broader alignment. Mr Bessent visited Tokyo in May, where he met the prime minister, Sanae Takaichi, and signalled his support for Governor Ueda. He has repeatedly called for faster BOJ rate increases, and a notepad photographed at a cabinet meeting in Camp David bore the notation "Buy Japanese Yen (JPY) $5-10 bil". On July 31st he posted on social media that he looks forward to seeing Mr Ueda at the G20 finance meeting in North Carolina at the end of August, calling the governor his "longtime friend" and praising the BOJ's "strong commitment to monetary and financial stability".

The reason for such sustained public diplomacy is not hard to see. A weak yen blunts the trade advantage from President Donald Trump's flagship tariffs. It also fuels Japanese import inflation, which makes life difficult for Ms Takaichi's government, even as it threatens to spark further instability in Japan's government-bond market - volatility that has already spilled over into US Treasuries, drawing Mr Bessent's ire. Washington has its own reasons to care about the yen.

To be sure, the BOJ faces genuine domestic pressure. The yen's weakness is importing inflation at a time when wages have yet to catch up. Mr Ueda's hawkish pivot, first evident in April, has moved the central bank into rare alignment with the Ministry of Finance (MOF). Some market observers now see a September BOJ rate hike as near-given, with both Mr Bessent and Atsushi Mimura, Japan's top currency diplomat, signalling that further tightening is expected.

The deeper problem is not the size of the next rate move. It is that the BOJ's independence is being quietly eroded by foreign pressure dressed up as friendship. A central bank's credibility rests on the market's belief that it will act according to its own assessment of domestic conditions. When the treasury secretary of the world's largest economy routinely endorses a foreign central banker and signals that further action is expected, the line between encouragement and coercion blurs. Even if the BOJ continues to raise rates, as its domestic mandate arguably requires, the market may begin to doubt whether those decisions are truly its own. Reuters Breakingviews calls it a no-win scenario: even raising rates could undermine belief in the BOJ's independence.

The situation is compounded by Tokyo's own fiscal policy. Ms Takaichi's expansionary fiscal and monetary stance is anathema to a stronger yen. Higher government borrowing and spending put downward pressure on the currency, which means the BOJ is expected to hike rates to compensate for the finance ministry's choices. That is fiscal dominance by another name: the central bank doing the heavy lifting for policies it did not choose. The joint US-Japan intervention only intensifies this contradiction, by raising market expectations that the BOJ must keep tightening, even as the government's fiscal direction points the other way.

The better answer would be for Mr Bessent to channel his concern about the yen into quieter diplomacy and for Japan's government to address the fiscal drivers of its currency's weakness. Coordinated intervention can calm a panic, but it cannot fix a structural imbalance. Repeated interventions, especially when they are funded in ways that signal hesitation rather than conviction, risk training markets to expect ever-larger doses of official interference. And the more the BOJ's policy moves look like a response to external pressure, the less effective they become as a tool for domestic price stability.

Central bankers do not need cheering from foreign capitals. They need room to do their jobs. Mr Ueda would be wise to remember that the best defence of the yen is not a notepad in Camp David. It is a monetary policy that the market believes is his own.