Speaker of the House Paul Ryan looks on as President Donald Trump speaks about tax legislation in November 2017. Photo: Drew Angerer/Getty Images

It is a foundational belief of Republican Party doctrine that tax cuts cannot have any adverse impact on the national debt. Indeed, Republicans have invented a new language in which budget deficit does not actually mean the difference between revenue and outlay at all. It is a term used exclusively to express panic over social spending.

Economists and intellectuals associated with the party are therefore required to, in essence, keep two different sets of books when discussing fiscal policy in public. In November, a group of Republican luminaries, including Michael J. Boskin, John H. Cochrane, John F. Cogan, George P. Shultz, and John B. Taylor co-authored an op-ed cheering on the Trump tax cuts. Isn’t it a little dangerous to permanently increase the deficit, especially during the peak of an economic expansion? Nonsense, they argued. The effect on interest rates of higher debt “is likely to be modest, given that the United States operates in an international capital market, which means that the impact of changes in interest rates resulting from greater investment demand and government borrowing are likely to be relatively small.” No need to worry your pretty little heads about interest rates, since international capital markets will supply as many buyers of Treasury bills as needed, forever. Party on!

Now that the Trump tax cuts have passed, though, they have pivoted to a message of deep concern about rising debt. Boskin, Cochrane, Cogan, Shultz, and John B. Taylor have written another op-ed. It applauds the tax cuts and calls for more. Yet it warns that the failure to cut social spending will lead to catastrophe. Including higher interest rates:

In recent months, we have seen an inevitable rise in interest rates from their low levels of recent years. Rising interest rates and increasing deficits threaten to build upon each other to send public debt spiraling upward even faster. When treasury debt holders start to doubt our government’s ability to repay, or to attract future lenders, they will demand higher interest rates to compensate for the risk. If current spending and tax policy continue unaltered, higher interest costs will have to be financed by even more debt. More borrowing puts more upward pressure on interest rates, and the spiral continues.

If, for example, interest rates were to rise to 5 percent, instead of the Trump administration’s prediction of just under 3.5 percent, the interest cost alone on the projected $20 trillion of public debt would total $1 trillion per year. More than half of all personal income taxes would be needed to pay bondholders.

Those international capital markets, which ensured us of low interest rates forever even with the higher deficits that would follow the Trump tax cuts, have somehow disappeared. In their place is a new world where suddenly interest rates may spike catastrophically with no warning. Immutable laws of economics have suddenly reversed themselves. Until it’s time for the next tax cut, when they will reverse themselves again.