THE Budget Act of 1921 requires the president to propose a budget, but Congress holds the power of the purse. Since Mick Mulvaney, the budget director, sketched out the Trump administration’s proposal in February, it has been clear that lawmakers would end up rewriting it. Mr Mulvaney wants immediate deep cuts across government that are unpalatable even to many Republicans. The fleshed-out version of the budget, released on May 23rd, features a new promise: to eliminate the budget deficit within ten years.

The president wants to leave Medicare, health insurance for the old, and Social Security (public pensions) untouched. As a result, achieving budget balance requires an unimaginably deep cut to so-called “non-defence discretionary” spending, which includes things like education, scientific research and diplomacy. This part of the budget would shrink by 41%, after adjusting for inflation, according to the Centre for Budget and Policy Priorities, a left-leaning think-tank. That greatly exceeds the deepest cut the administration had already proposed for 2018, of about one-third, to the State Department.

Entitlement programmes for working-age people would be slashed. Federal funding for Medicaid, health insurance for the poor, would eventually fall by nearly half (a greater cut than in the House Republicans’ health-care bill). The budget for Supplemental Nutrition Assistance, which helps the destitute buy food, shrinks by a quarter, as part of the burden of supporting the poor is shifted to the states.

Yet even all this would be insufficient to eliminate the budget deficit, which is forecast to swell to 5% of GDP by 2027 under current law (because of increasing spending on the aged). To get the budget to balance, Mr Mulvaney also assumes the economy will grow by 3%, a target that will be difficult to reach in the demographic headwinds. Fast growth fills the government’s coffers by about $2trn over a decade.

The problem is that Steve Mnuchin, the treasury secretary, has already banked that $2trn to pay for the tax cuts that are supposed to spark the 3% growth in the first place. Another contradiction is that the budget predicts growing revenue from the estate (inheritance) tax, which it promises to abolish. It is one thing for the executive and legislature to disagree. But the Trump administration has produced a blueprint that contradicts itself.