When he said on Sunday that he couldn’t vote for the current version of President Biden’s social spending and climate change bill, despite months of painstaking negotiations, West Virginia Democratic Senator Joe Manchin put the expansive package on life support and imperiled a key part of Biden’s agenda. To salvage the bill, Democrats will have to talk Manchin out of his misguided belief that the legislation would harm the economy by sending inflation soaring while rewarding wrongdoing parents and lazy workers — ideas that have already been disproved by economists, independent policy researchers, and data.

The alternative is letting the whole effort collapse. In a 50-50 Senate where no Republicans are expected to support the legislation, Manchin’s vote is needed to approve the package.

According to a Washington Post report, Manchin’s opposition to the bill is based on the size and scale of its climate measures and his disapproval of extending paid leave and the expanded monthly child tax credit of up to $300 per child, which expired this month.

Manchin reportedly also privately raised concerns with his colleagues that a provision of the bill giving four weeks of paid family and medical leave to all US workers would be abused by some to go on deer hunting trips. Manchin also reportedly worried that the expanded child tax credit was being used by parents to buy drugs.

Let’s start by disabusing that last assertion, which harkens back to the derogatory “welfare queen’’ myth peddled by Ronald Reagan and others in the 1980s, when entitlement programs were a political football.

The truth is that the expanded child tax credit, first implemented in July as part of the emergency pandemic stimulus bill, reduced childhood poverty by 40 percent, according to a Columbia University study. Extending the benefit could help keep millions of children out of poverty permanently, according to an analysis by the Center on Budget and Policy Priorities.

With the Omicron variant surge causing renewed economic uncertainty, this is no time to cut that lifeline. In a recent survey by family advocacy nonprofit ParentsTogether Action, half of the parents and caregivers polled said the loss of the expanded child benefit would make it harder for them to meet their families’ most basic needs: food, housing, and child care. In fact, 15 percent of respondents said the loss would require them to cut back on their work hours because child care alone would become prohibitively expensive.

Manchin is also wrong in dismissing the size and scope of climate measures in the bill as seeking to do too much, too fast. As climate policy experts have noted, these measures — designed to provide long-term incentives to energy developers, auto manufacturers, and others to invest in cleaner power sources — cannot simply be scaled back without it having a major impact on their effectiveness.

The version of the bill at which Manchin balked, which included $555 billion in clean energy and emissions reduction measures, had already been slashed far below what experts said was needed for the United States to fully meet its greenhouse gas-cutting obligations under the Paris Climate Agreement.

While Manchin’s support for — and from — the coal industry has always been a major basis of his opposition to climate measures, this week the United Mine Workers of America urged him to reverse course and support Build Back Better.

“The bill includes language that will provide tax incentives to encourage manufacturers to build facilities in the coalfields that would employ thousands of coal miners who have lost their jobs,’’ said the union’s president, Cecil E. Roberts, in a statement after Manchin rejected BBB. “We support that and are ready to help supply those plants with a trained, professional workforce. But now the potential for those jobs is significantly threatened.’’

Manchin’s rejection of the bill also caused electric vehicle stocks to tumble, impeding carmakers’ ability to spur customer demand in a way that will only make it harder for those companies to hire and retain workers.

The failure to extend paid leave also will have a negative impact on small businesses. Pandemic-related closings, supply chain problems, and other obstacles have created a particular urgency for small-business owners, 65 percent of whom support the four-week family and medical paid leave provision that Manchin eschews, according to a survey by Small Business Majority.

Even a seasoned lawmaker can make mistakes. If Manchin honestly believed the bill would harm the economy, the facts prove his theory wrong. That means there is nothing stopping him from changing his mind, or at the very least returning to the negotiating table in the new year ready to work in earnest with the White House to get the bill across the finish line.

Editorials represent the views of the Boston Globe Editorial Board. Follow us on Twitter at @GlobeOpinion.