Rotherham MP occupies the office where every persuasive plea for extra funding will eventually land
After a fortnight in No. 11, John Healey has probably discovered that every spending decision creates another adversary
Only a few weeks ago, many of the challenges occupying John Healey’s attention were thousands of miles away.
Russia, North Korea and Iran. As Defence Secretary, the threats were external and the political argument was relatively straightforward.
Britain faced a more dangerous world and Britain's Armed Forces needed the resources to match.
Now his biggest headaches are much closer to home. They arrive carrying ministerial red boxes rather than military intelligence.
The irony is almost irresistible.
Only weeks ago Healey was among those arguing that more money should be found for his own department.
Today the Rawmarsh and Conisbrough MP occupies the office where every persuasive plea for extra funding eventually lands.
He has spent the first fortnight of his Chancellorship discovering that almost every Cabinet colleague now sounds remarkably like John Healey did a month ago.
Health needs more. So do housing, social care, local government and transport.
Every minister arrives armed with convincing figures, genuine pressures and a compelling case that their department cannot possibly manage without just a little extra.
That innocent little word, "just", must already have become one of the Chancellor's least favourite words in the English language.
"Just another £2 billion." "Just enough to honour a manifesto commitment." "Just enough to get us through the Spending Review." Multiply "just" by every department in Whitehall and the bill soon becomes anything but modest.
Healey (66) knows the Treasury as well as most politicians, having served there earlier in his career, so none of this will have come as a surprise.
Even so, there is a world of difference between understanding the theory and living the reality.
Reading a submission is one thing. Looking a Cabinet colleague in the eye and saying, "Not this year," is quite another.
The walk from the Ministry of Defence to the Treasury is little more than a stroll across Whitehall.
Politically, however, it is one of the longest journeys in government.
Healey has crossed from the department that asks for more money to the department that has to decide who cannot have it.
That is why Chancellors are judged differently from almost every other minister.
Defence Secretaries, Health Secretaries and Education Secretaries are expected to champion their cause.
The Chancellor's duty is rather less comfortable. He must challenge every cause, including those he may once have championed himself.
For now, Healey and the Prime Minister appear firmly in step, presenting a united message that new ambitions must be financed from within existing budgets.
That unity will be tested not by speeches or joint letters but by arithmetic.
Every new promise eventually arrives on the Chancellor's desk with a price tag attached. Every additional pound for one department is a pound unavailable to another. In the Treasury, arithmetic has the final word.
Spending departments deal in priorities. The Treasury deals in limits.
Every road to the Treasury is paved with good intentions. Most end with the words, "We simply can't afford it."
Politics is often about promises. The Treasury is about choices. Somewhere between those two lies John Healey's new job.
The Rotherham family man spent years arguing that Britain should spend more on what mattered most.
Today he has to tell colleagues, many making arguments every bit as passionate as his own once were, that there simply is not enough money to satisfy them all.
That is the Chancellor's burden. Success is measured not by the number of people he pleases, but by the number he disappoints.