IN APRIL America’s unemployment rate fell to 3.9%, its lowest since December 2000. That is not good enough for Democrats eyeing the 2020 presidential race. Senator Bernie Sanders recently promised to introduce a bill guaranteeing every American a taxpayer-financed job, should they want it. His colleague, Senator Cory Booker, has already written a bill which would test such a policy in 15 places with high joblessness. Senators Kamala Harris, Elizabeth Warren and Kirsten Gillibrand, three other potential presidential contenders, are co-sponsors. Ms Gillibrand will reportedly soon pen her own plan, too.

For a long time, so-called full employment was the holy grail of economic policy for Democrats. In his 1944 state of the union address, President Franklin Roosevelt proposed a “second bill of rights” that would guarantee the right to work. In 1946 Congress passed the Employment Act, which declared it the responsibility of the federal government to “use all practicable means” to ensure there were jobs for everyone who was willing to work. The Keynesian demand management that followed kept unemployment fairly low for several decades. But even as the post-war consensus on economic policy was collapsing in 1978, Congress passed the Humphrey-Hawkins Full Employment Act, which set a goal of 3% unemployment by 1983. The act, much of which turned out to be toothless, also asked the government to create a “reservoir of public employment”. Had the left got its way, the welfare reform President Bill Clinton signed in 1996 would also have guaranteed a minimum-wage job, as a last resort, for those leaving the welfare rolls.

The timing of Democrats’ revival of the idea of a jobs guarantee is strange because many economists, including those at the Federal Reserve, think that the economy is beyond full employment. To their mind, the unemployment rate is unnaturally low, and if policymakers try to sustain it via stimulus, inflation will result. If they are right, today’s joblessness is the result of structural factors, such as insufficient skills, unrealistically high wage demands, or an unwillingness of workers to leave stagnant areas. It is not the involuntary unemployment, resulting from a weak economy, which so concerned Keynes.

Still, a strong economy does not make a jobs guarantee pointless. It would reduce structural unemployment. If recession did strike, more government jobs would both provide a safety net for workers and automatic stimulus to demand. Most important, guaranteed alternative employment would raise the bargaining power of unskilled workers. They could use it as leverage when negotiating with their existing employers. Mr Booker’s plan would offer parental leave, health insurance and pay its participants a wage that would eventually rise to $15 an hour. Private employers would have to compete with this generosity when hiring workers. That appeals greatly to those who fear automation and the gig economy are combining to create a glut of low-paid workers without bargaining power (in Britain, such workers have been dubbed the “precariat”).

Low-paid jobs are concentrated in the food, hospitality and retail industries. Some employers would match the government’s terms. It is easy to imagine, say, restaurants in San Francisco or New York, whose wealthy customers may not balk at higher prices, paying their workers more and passing the costs on to customers. But others, such as those in the beleaguered retail industry, could struggle.

The policy’s supporters compare it to the minimum wage, which they say has not much dented employment even when set high. But that has typically been in rich cities. Were the terms of employment as generous as Mr Booker wants across the country, the impact on the government payroll could be huge. About half of America’s 148m workers earn less than $15 per hour. In some southern and south-western states, the figure is almost 60% (see chart).

That would not be a problem, were the government capable of productively employing tens of millions of new workers. Supporters of the policy envisage armies of labourers erecting infrastructure, caring for children and cleaning up the environment. Yet some of these jobs are skilled. Others are unsuitable for a programme that would face high turnover in a strengthening economy, and sudden influxes during recessions. In any case, it is hard to imagine the government operating the programme efficiently, even if the job of running projects were delegated to states, as proposed by the Centre on Budget and Policy Priorities (CBPP) a left-leaning think-tank. Government at all levels employs 22.3m Americans. Even if the CBPP’s estimate of take-up of about 10m is right, it would represent nearly a 50% expansion of the government payroll. It is not clear whether these workers could be sacked if they performed poorly.

It goes without saying that Congress is unlikely ever to authorise such an intervention, not least because it would be expensive. The CBPP’s conservative calculation puts the bill at $543bn (2.7% of GDP)—about one-and-a-half times what the federal government spent on Medicaid in 2017. Mr Sanders has not yet set out where he will find the money. Raising that much cash with only new taxes on the rich will be difficult (although a jobs guarantee could cause other welfare spending to fall).

A more realistic route to improving the lot of low-skilled workers would be to beef up labour market regulation, and to subsidise unskilled jobs to the degree necessary to keep them profitable for employers. This could be achieved incrementally, for example by expanding tax credits for low earners. Many Democrats claim that such schemes subsidise big corporations, like Walmart, to pay low wages. It is true that firms see about a third of the benefit of such subsidies, according to the best research on the subject. But unlike a jobs guarantee, they do not risk the colossal waste of resources that is likely from a huge expansion of the government payroll.

That will not worry Democratic presidential hopefuls, who are happily playing to the left of the party. They seem most concerned with guaranteeing a job for themselves—in the Oval Office.