Vermont Sen. Bernie Sanders (I) criticizes Democrats for lacking the courage to think big. But it takes no courage to promise impossible levels of new spending and programs that could not work as advertised. It takes courage to level with voters. Mr. Sanders’s rivals for the Democratic presidential nomination have done far better at that.

Fresh off a big win in the Nevada caucuses, he released on Monday his latest massive spending proposal, a plan to enable all Americans to get child care. It is similar to the universal child-care plans that Sen. Elizabeth Warren (D-Mass.) and former South Bend, Ind., mayor Pete Buttigieg (D) previously rolled out, except it would cost more than twice as much.

Each candidate’s plan would provide universal access to child care. Each would rely on a mix of organizations — from small, home-based facilities to large day-care centers to public schools. And each would apply new standards to the child-care industry and raise the pay of child-care providers.

But Ms. Warren’s and Mr. Buttigieg’s plans would cost $700 billion over a decade, and Mr. Sanders’s $1.5 trillion. What’s the big difference? In large part, it is that Mr. Sanders would make government-sponsored child care free to all, even the wealthiest of families. Ms. Warren and Mr. Buttigieg would ask families that could afford to pay something to do so. The Warren plan, for example, would offer free services for those who make up to twice the poverty level — or about $50,000 for a family of four. Everyone else would pay something, their contribution determined on a sliding scale based on their income, though no family would have to pay more than 7% of its income.

Mr. Sanders says he can pay for his unnecessarily expensive approach with money he would raise from his proposed wealth tax. But economists calculate a gap of $1 trillion or more between what his wealth tax would raise and what he claims it would raise. Given the massive shifts in taxation that Mr. Sanders is already proposing, meeting the shortfall with additional taxes would be extremely hard. Even if Mr. Sanders led a political revolution that reshaped Congress, making his plans more politically viable, the country does not have an unlimited supply of money that can be diverted into the federal treasury without consequences for economic growth. True progressives recognize that federal money is scarce and must be spent carefully, with the poorest first in line, so that many needs can be met.

Mr. Sanders presents himself as the only one who really cares about issues such as health care, climate change and pre-K. But other Democratic candidates, not Mr. Sanders, are treating these issues with the seriousness they deserve.

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