Democrats are rushing to finish a massive spending bill before President Joe Biden leaves for international meetings later this week. They are at risk of producing legislation that is so compromised and slapdash that it would amount to a tragic missed opportunity. On the spending side, Democrats might skimp on permanent structural reforms so they can fund more programs that are smaller or short-term. On the revenue side, their plans might easily result in massive new debt. This is not what Mr. Biden promised.

Democratic holdouts Sens. Joe Manchin of West Virginia and Kyrsten Sinema of Arizona demanded a smaller bill than most in their party favored. In response, Democrats have struggled to prioritize. They should have forgotten about spending yet more money on already highly subsidized senior health care, focusing instead on permanently shoring up the Affordable Care Act and Medicaid programs for working-age people who would otherwise struggle to get even basic coverage. Yet some form of Medicare expansion for retirees is still on the table, while Democrats are discussing ACA and Medicaid fixes that might run only a few years.

Similarly, Democrats might expand the child tax credit for perhaps only a single year. The expanded credit could halve child poverty. A long-term expansion should take precedence over a federal pre-kindergarten program or expanded housing aid.

If temporary benefits expire as written, the nation will derive little long-term good for its money. Democrats might bet that future Congresses — even those run by Republicans — would not want to revoke popular benefits. If that is so, the Democrats’ bill would effectively write a suite of expensive new programs into the law without long-term revenue streams to back them. That is largely because Ms. Sinema derailed Democrats’ plan to roll back President Donald Trump’s ruinous tax cuts, which were massive giveaways to the rich at a time of high wealth inequality and big budget deficits. Rather than modestly raising the individual and corporate tax rates, she appears to have forced Democrats into embracing a complex billionaire tax that the Supreme Court might well strike down. Another big revenue source, pumped-up Internal Revenue Service tax enforcement, may well fail to bring in the massive amounts Democrats claim it would. These squishy pay-fors seem designed to provide an illusion of fiscal integrity that could quickly evaporate after the bill passes.

Meanwhile, Mr. Manchin appears to have forced the Democrats to drop their central climate change policy, a standard that would have pushed utilities to steadily adopt clean energy, leaving only a laundry list of expensive green subsidies in the bill. This would not and should not impress other nations that have adopted real carbon caps to guide their economies.

There is still time to improve this bill. Democrats should cut more programs and make the ones they embrace effective and durable. They should find more believable pay-fors. And they should try again to develop a strong climate policy that Mr. Manchin can live with.