CONGRESS writes the budget, not the president. That means Donald Trump’s radical budget blueprint, released on March 16th, is unlikely to be implemented in full. Yet it does reveal his priorities, and lawmakers will probably end up backing bits of it. The blueprint sets out the deep cuts Mr Trump wants to make to Washington’s bureaucracy. It contains plans for spending, but not tax.

Most eye-catching are a 31% proposed cut to the Environmental Protection Agency and a 28% cut to the Department of State. Much of the latter cut would fall on foreign aid. In every other department, Mr Trump would let the axe fall on spending that Republicans have long disliked. For example, funding for the Corporation for Public Broadcasting, which helps fund public radio, would disappear, as would the National Endowment for the Arts. The document implies that others should fill the gap left by the federal government. Sometimes, it points to state governments, as with “local environmental efforts and programs” such as restoring the Chesapeake Bay. Elsewhere, it is foreign governments who should pay up. For example, America would not contribute more than 25% to UN peacekeeping costs, down from almost 29% today. The budget is avowedly “America first”.

During his campaign, Mr Trump promised to eliminate waste and inefficiency in the federal government. But the departments that he now wants to gut have already faced real terms cuts of 10%, on average, since 2010, partly because of the Budget Control Act (sometimes called “the sequester”). These cuts, which also applied to the defence budget, kicked in when lawmakers could not reach a better deal to reduce the deficit. As a result, there has already been pressure to find savings. By “waste”, Mr Trump seems to have meant programmes that he does not like. For example, it is not the efficiency of spending on public broadcasting that Republicans object to. It is the fact that the federal government is funding public broadcasting at all.

The freed-up cash would be spent on defence. (“This is a hard-power budget” declared Mick Mulvaney, Mr Trump’s budget chief, “it is not a soft-power budget”.) The reallocation of the cash means nothing is saved overall. Yet, strangely, it begins with the familiar Republican lament about budget deficits. Mr Mulvaney writes the national debt is a “crisis…for every citizen”, that “American families make tough decisions every day about their own budgets” and that “it is time Washington does the same”.

In fact, Mr Trump is likely to dodge those tough decisions. America’s long-term fiscal problem is driven by its ageing society. More old people means more spending on Medicare, health insurance for the old, and on Social Security (public pensions). No serious attempt to reduce the public debt can succeed without either cutting these entitlements or raising taxes. But Mr Trump has promised to protect that spending, to cut taxes, and to increase spending on infrastructure, to boot.

His budget unwittingly proves how unrealistic those goals are in combination. Even with deep cuts to the State Department, environmental protection and so on, the White House is only able to fulfil one of its aims: more defence spending. And it provides less money than hawks, like Senator John McCain, insist is necessary. Where, then, is the money for everything else, and for closing the deficit, going to come from? Borrowing is forecast to be $559bn in 2017. Even if Mr Trump abolished all government departments—leaving Washington paying only for entitlements, debt interest and defence—a deficit would remain.

The answer will be revealed when the White House unveils its full budget plan, in May. It could be that Mr Trump will make his sums add up with fanciful projections for economic growth. That might work for now. But later, when the boom does not materialise, writing a budget will be harder still.