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).