IMAGINE you have developed a serious weight problem. Things have been going badly for you, and as a result you have been piling on the pounds; in the past three years your weight has ballooned by a shocking 10% a year. Your advisers all say that this will give you a heart attack: not immediately, but in the next decade or so. What do you do? Not many doctors would recommend a diet confined to items that make up only an eighth of your consumption (and were in any case often rather good for you), while slyly sticking to a plan to increase gradually the number of cream buns and cheeseburgers you eat every day. Yet that is exactly what Barack Obama has prescribed for the bloated American government.

This week the president presented his draft budget for 2012. In its obfuscations, half-truths and omissions it is perhaps no worse than the budget proposed by the supposedly “small government” Republicans, which likewise concentrates on harsh cuts to small subsections of government spending. But from a true reformer's perspective its only virtue is that investors in American treasuries may be so panicked by its inadequacy that, at last, change may result.

Even though the economy has been out of recession for more than a year, America's deficit is bigger this year than last, and Mr Obama's budget still sets it at well over $1 trillion next year too. Yet the document supposedly cuts the deficit from 11% of GDP this year to 3.1% by 2021. That number is not credible. First, it is based on growth figures that are better than those projected by either the non-partisan Congressional Budget Office or private-sector forecasters. Next, Mr Obama assumes that he will be able to increase current taxes on the rich in 2012, despite the fact that he was unable to do just that last year when his party still controlled the House of Representatives; now he will have to deal with Republicans who are opposed to it. Other revenue-raisers look similarly fanciful.

Finally, the budget plans to find $400 billion of savings in “non-security discretionary” spending over the next ten years. This category accounts for only about 12% of the federal budget, including worthy things like education, infrastructure investment, environmental regulation and many forms of aid to the poor. The cuts that Mr Obama is proposing are a very mixed bag. Some will be blocked by Democrats, others by Republicans. True, the latter have their own long wishlist of cuts, but there is precious little overlap.

Go on, Supersize me

Let's indulge Mr Obama in his fantasy economics: imagine that he does reduce the deficit to 3.1%. Supposedly, that would stabilise government debt: but it would do so at a dangerously high level of around 80% of GDP, and as interest rates rise the target will become much harder to hit. And that is before you consider the biggest problem of all: as more and more baby-boomers retire (the first started to do so this year), their demands for pensions and government-provided health care will start to push the deficit sharply up again after that.

Indeed, the real problem with both Mr Obama's budget and the Republicans' proposals is not so much the half-truths and fibs within them, as all the things they both left out. America needs to simplify its tax system and (slightly) increase its overall tax take. It needs to rein in its defence spending, which is currently equivalent to that of the next 20 countries combined. And it needs to tackle the gathering surge in entitlement costs. All these recommendations were made by the deficit-reduction commission that Mr Obama himself set up, but his budget conspicuously fails to take up any of them. Other debt-burdened Western countries have embarked on a stringent diet. America continues to gorge.

Why not show a little leadership? In a routine that is becoming depressingly familiar, Mr Obama's camp argues that the time for these things is not yet ripe. Rather than set out any bold proposals of his own, the president would rather leave it to Congress. Once congressional Republicans and Democrats have found some common ground, he will work with them.

In fact, a small group of brave senators from both parties is already toiling away to just that end. But neither the president nor Republican leaders have had the courage to support them. In the absence of statesmanship, the chances are that only a crisis in the bond markets will provide the necessary impetus. Economic management by fiscal heart attack is not a very prudent remedy.