President Trump has a $2 trillion hole in his fiscal policy proposals. His numbers don’t add up. This creates a conflict between two of his fiscal policy goals: tax reform and balancing the budget.

Let’s look at three elements of President Trump’s economic policy and how they interact:

  1. Last month he proposed tax reform with most of the key numbers left blank.
  2. Today he proposed a budget that claims to reach balance in 2027 (year 10).
  3. His budget assumes his economic policies would increase economic growth by a lot, to 3 percent per year.

In addition to proposing a budget that purports to balance in year 10, today Trump Budget Director Mick Mulvaney told us one key new fact about tax reform: the Administration now assumes tax reform will be debt neutral. Director Mulvaney used this to explain why the President’s top fiscal priority, his tax reform proposal, which would involve trillions of dollars of changes to tax policies, was omitted from the President’s budget. This omission is, to say the least, odd.

There is significant public debate about whether Team Trump’s aggressive growth assumption is reasonable given the policies he has proposed. For now let’s set aside this critical question and pretend it’s reasonable. Let us assume President Trump’s economic advisors are right, that his policies would result in 3% real growth per year, and that this faster growth would benefit the budget. Let us further assume their estimate of the [budget] Effect of economic feedback is correct. You can see it in today’s budget proposal (Table S-2, near the bottom of page 26, which is page 32 of the PDF). President Trump’s advisors assume this faster economic growth will reduce the budget deficit by $496 billion in 2027, their target year for balancing the budget.

The President’s balanced budget claim depends on this $496 billion effect of economic feedback in year 2027. They assume almost $500 billion of government spending bills in 2027 will be paid from additional cash inflows that result from higher government revenues resulting from faster economic growth, rather than from cash borrowed from financial markets. Faster growth —> higher government revenues —> less need for government borrowing to pay spending bills —> lower deficits and debt & budget balance in year 10.

This $496 billion is a really big number for a single year. For comparison, it is almost twice as large as the $251 billion the president proposes to cut non-defense discretionary spending in that year. It is three times as large as the $165 billion the budget proposes to save in Medicaid in that same year.

On that same line of Table S-2 you can see Team Trump assumes economic growth means the federal government will need to borrow $2 trillion less over the next ten years. That equals 6.6% of GDP in 2027, an enormous amount. When Director Mulvaney says President Trump’s budget would reduce debt/GDP from 77% this year to 60% in 2027, about a third of that reduction is from this single assumption.

So far, so good. Items (2) and (3) work together: the balanced budget promise and the positive budget effect of the 3% growth assumption, which for now we are stipulating is valid. The problem is fitting debt-neutral tax reform into this puzzle as well.

We don’t know how much the tax reform proposal would cut taxes because in April President Trump did not provide sufficient detail to estimate it. The President’s campaign proposal was roughly a $6 trillion gross tax cut. Let’s make a wild guess and assume his new proposal is smaller, a $5 trillion gross tax cut. The concept that follows is what matters, not the actual gross number.

If your tax proposal, which you left out of your budget proposal, is debt neutral, then you need to have the same amount of new revenues to fully offset the revenue lost to the government from your proposed gross tax cut. In our example you’d need to have $5 trillion in new revenues over ten years to combine with $5 trillion of gross tax cuts to result in a debt-neutral package. In theory, this offsetting revenue can result either from proposed tax increases or from the higher revenue that results from economic growth, or from a combination of the two. You’d also need to match your revenue loss and revenue gain in 2027 so that your proposal doesn’t affect balance in that year.

In our example, if you combined $5 trillion of gross tax cuts with $3 trillion of tax increases, your tax reform package would be a net $2 trillion debt increase over ten years. If, however, your tax cuts would also result in faster economic growth, and if you think that economic growth would result in an additional $2 trillion of government revenues, then your tax package in total would be fully offset and debt neutral. This dynamic scoring of tax reform would make it significantly easier to enact debt-neutral tax reform, because you would need to add only $3 trillion of painful tax increase policies to a package that includes $5 trillion of gross tax cuts that people and businesses like and support.

But you cannot have it both ways. If you try, you are double counting. Either the $2 trillion of added cash inflows resulting from faster economic growth can pay for more government spending and reduce the need for government to borrow, or that $2 trillion can replace the cash lost to the government from cutting taxes and reduce the size of painful tax increases you need to propose. Arithmetic forces you to choose one goal or the other.

Last month Secretary Mnuchin counted the (then unspecified) positive budget effects of economic growth to help offset their tax reform package. Today Director Mulvaney counts those $2 trillion of extra revenues to reduce government borrowing and achieve a balanced budget. Logic requires they choose one or the other, but today they chose both and Director Mulvaney said that choice was deliberate. There will be only one $2 trillion stream of cash (if you even believe it’s that large). By claiming they can do two things with each dollar of cash they have left a $2 trillion hole, either in the Trump balanced budget proposal or in the Trump debt-neutral tax reform proposal.

If they’re going to use growth effects to help balance the budget as proposed today, then Secretary Mnuchin either needs to convince President Trump to support $2 trillion of additional tax increases to keep tax reform debt neutral, or they need to support significantly smaller gross tax cuts. Secretary Mnuchin has so far opposed the two biggest tax increases needed for a big debt-neutral tax reform: a border adjustment tax and eliminating the business deduction for interest expenses (which, coincidentally, would together raise about $2 T of revenues over 10 years). If they want to use dynamic scoring to make tax reform easier to enact, then President Trump and Director Mulvaney do not have a balanced budget proposal until they find almost $500 B of additional deficit reduction in 2027.

You can’t have it both ways, and $2 trillion is a big hole to fill.