Two problems. Trump first rejected this plan as too complicated, then decided he favoured it, and now has turned agnostic. It seems that major importers, most notably Walmart and other retailers, met with the President at the White House and informed Trump that the Ryan plan would force them to raise prices by 20 per cent, which would hit Trump’s supporters where it hurts — in their wallets and pocketbooks. That is a bit disingenuous. For one thing, the tax would apply to the cost of the imported goods, not to the higher final sales prices. For another, economists who favour the import levy argue that it would strengthen the dollar sufficiently to offset the tax, since a stronger dollar makes imports cheaper. Walmart employs 1.4 million workers, 1 per cent of the US working population — voters prepared to punish legislators who vote against their employer’s interests. No surprise that several senators have expressed an unwillingness to risk a forced return to the private sector by betting that the economists’ models are better than, say, the ones that failed to predict the financial crisis.

For the moment, the border adjustment tax has been released from intensive care, but not because its prospects have improved. Rather, it is considered DOA, beyond resuscitation. Worse still, the most efficient possible alternative source of revenue, a carbon tax, is unlikely to seem attractive to a President who regards climate change as a “hoax”.

So the question now before Trump and the congress is how to raise the revenues needed to offset a reduction in corporate tax rates. One source might be the feature of the tax code that allows interest to be treated as an expense, but denies such treatment to dividends paid to holders of a company’s equity. This gives corporations an incentive to borrow rather than raise equity capital, to increase the risk they face of a downturn that impairs their revenues, as interest must be paid, and dividends can be reduced in times of stress. Levelling the playing field, treating interest payments the same way as dividends are treated, would discourage dangerous over-leveraging.

But property developers are among the most highly leveraged of entrepreneurs; the deductibility of the interest they pay on the debt load under which they usually labour is crucial to their financial success. And when their business turns down, bankruptcy results, as Trump, known in his business days as “the King of Debt”, well knows.

This change has many proponents, including Speaker Ryan, who couples it with allowing an immediate write-off of equipment purchases, and Stephen Moore, the economist who advised Trump during his campaign. But the former property developer now splitting his time between the White House and Mar-a-Lago is not among them. “He hated the idea,” Moore told an interviewer. Not necessarily because he is acting in his narrow self-interest, although Democrats are accusing him of doing just that, but because he sees the world, and its economic engine, through the lens of a lifetime as a property developer. Take away their tax break and there will be fewer apartment towers built and fewer construction jobs for the nation’s hard-hats, fewer hotels to provide jobs for low-skilled workers.