Sen. Cory Booker (D-N.J.) says he will announce a job guarantee pilot program. (AP Photo/J. Scott Applewhite)

An idea for decades confined to academic circles and lefty fantasies burst into the mainstream of American politics this week, with the backing of four rumored Democratic candidates for the 2020 presidential nomination.

The proposal — for a “jobs guarantee” in which the federal government promises every American a job — has won the support of Sens. Cory Booker (D-N.J.), Kirsten Gillibrand (D-N.Y.), Bernie Sanders (I-Vt.) and Jeff Merkley (D-Ore.), with both Booker and Sanders promising to announce proposals in the coming months. At least two other Democratic senators have been briefed on the idea by Darrick Hamilton, an economist at the New School in New York who has pushed the jobs guarantee program.

The sudden interest in the ambitious, sprawling jobs guarantee plan has revealed the broader fissures in a Democratic Party that continues to wrestle with the appropriate government footprint in Americans' health care, college costs and a slew of other issues. Among the main questions is whether Democrats should advocate universal programs or focus on advancing more targeted approaches to ameliorating specific social ills.

The debate has also showed the extent to which Democratic politicians believe that the electorate is hungering for radical changes to the American economy — even as unemployment continues to fall and growth appears robust — and is willing to entertain previously obscure ideas to bring them about.

“Many politicians in the [Democratic] party have picked up on the hunger for ambitious, redistributive economic proposals,” said Dave Hopkins, a political scientist at Boston College. “But is this a plan that will help win a Democratic primary, or is it a plan that will win back Trump voters in a general election?”

Job guarantee supporters have touted polling that they say shows support for the program above 50 percent in all 50 states, but a number of Democratic officials and center-left pundits say it would be prohibitively expensive and too unwieldy to administer.

“I don’t think it is a good thing for the Democratic Party to look or sound like drunken sailors,” Rep. Gerald E. Connolly (D-Va.) said about a series of ambitious policy proposals released by Senate Democrats that do not explain how they will be paid for. “We have to be the party of fiscal responsibility, especially given the fact that the Republicans have opened that possibility for us, maybe in a more viable way than they had in the past.”

Pundits and experts have argued this week over the economic merits of the federal government guaranteeing a job. The program would produce some welcome public sector jobs, but some economists fear it could also funnel people into work that is either unnecessary for the broader economy or for which they are not qualified.

They say the private sector creates jobs to meet a consumer demand of some kind in the economy, while the government creates public sector jobs for certain projects with a social goal, such as to monitor plane traffic or oversee public parks. Promising to put people in jobs simply for the purpose of doing so risks creating mismatched incentives, these critics warn. Others on the left fear the idea of tying government benefits to work.

Supporters also like to say that a job guarantee will balance the ups and downs of the economic cycle, with enrollment rising during economic downturns and falling when private sector growth is strong. But some argue that such as promise contradicts plans to use the jobs guarantee to bolster elder care, teaching and child care — work that is not supposed to be subject to business cycles and that requires long-term commitments and training.

“I don't think that jobs in the public sector that produce valuable investments should ebb and swell in the way that would be necessary for them to be part of a 'job guarantee,'" wrote Josh Bivens of the Economic Policy Institute, a left-leaning think tank, in arguing that a large investment in public sector jobs would be better than an outright jobs guarantee.

Supporters counter that job guarantee proposals can help beat back skyrocketing inequality in income and wealth, as well as decades of stubbornly stagnant wages for Americans. Income growth has slowed dramatically for 99 percent of Americans over the last three decades, and job guarantee advocates say their plan would force employers to raise wages. (The job guarantee programs call on the federal government to pay $15 an hour and offer health care and leave benefits.)

The plans would also create big new federal investments in projects designed at the local level. According to an early draft of his plan, Sanders's jobs guarantee would fund hundreds of projects throughout the United States aimed at addressing priorities such as infrastructure, care giving, the environment, education and other goals — something similar to the AmeriCorps program that funds thousands of young Americans' work in nonprofits, but on a much bigger scale.

“The Democrats are starting to realize we need to change the explanations for poverty and inequality,” said Hamilton, the New School economist who favors a jobs guarantee. “The idea of disciplining the poor to engage in behaviors that advance them is wrong, and Democrats now are shifting.”

They also say the politics are on their side. Sean McElwee, an activist at the progressive polling and analysis firm Data for Progress, said 52 percent of the country supports a job guarantee, with just 29 percent opposed. The issue enjoys unusually high support from members of both parties, according to McElwee.

“This issue has 50 percent support already,” said Josh Miller Lewis, a spokesman for Sanders. “And there has not been a single national politician talking about it in the last 40 years.”