For a moment, progressives seemed to have a dream opportunity to imprint their vision on the country. Democrats in March muscled through a big covid-19 relief bill on a party-line vote. The party seemed unified enough to leverage its thin majorities, as senior lawmakers prepared infrastructure and social spending bills that would cost trillions.

These dreams were never realistic, and they are now evaporating. But many progressives are having trouble accepting this, looking for gimmicky ways to enact broad structural change despite centrists’ objections.

To address the demands of key moderates, Democrats must cut back their big social spending bill from $3.5 trillion to $2 trillion or less. While all seem to agree that there is no way around slashing the price tag for Sens. Joe Manchin III (D-W.Va.) and Kyrsten Sinema (D-Ariz.), they disagree on how to do it. House Speaker Nancy Pelosi (D-Calif.) sent a letter to lawmakers last week arguing that Democrats should “do fewer things well.” House progressives responded with a letter arguing that Democrats should not cut programs but merely fund all of them for a shorter period of time. “This is our moment to make the President’s vision a reality,” the letter read. “This bill offers us a chance to fundamentally transform the relationship between the American people and their government.”

But that is not what President Biden promised when he ran for president. Mr. Biden handily beat the left’s candidate, Sen. Bernie Sanders (I-Vt.), in the Democratic primaries, arguing that one need not stage a revolution to do good. He spoke about returning normalcy and competence to Washington, not renegotiating the social contract.

To be sure, Mr. Biden emphasized certain policy goals, particularly addressing climate change. Democrats still have a chance to make concrete progress on climate, family, health and education issues — if they set aside grandiose ideological ambitions and prioritize. They do not need to expand Medicare for seniors who already have ample benefits; shoring up the Affordable Care Act for Americans of working age is a higher priority. They do not have to provide universal free community college when enhanced Pell Grants can pay the neediest Americans’ tuition bills. They can put stricter income limits on the child tax credit, ensuring that it still cuts child poverty without wasting taxpayer money on higher-income people.

Progressives’ plan to fund everything for fewer years would risk the sudden expiration of social programs in a relative heartbeat. To the extent progressives believe that future Congresses would extend those benefits, they favor budget cheating, making it seem as though their agenda is relatively inexpensive when the low price-tag simply reflects an unusually short spending window. If Democrats used 10 years of new revenue to finance five years of new spending, that would compound the misrepresentation.

This does not mean Democrats should settle for little. If the 2020 election was not a vote for revolution, neither was it an endorsement of stasis. Mr. Biden promised that a return to normalcy would produce tangible results. Mr. Manchin’s reported opposition to acting ambitiously on climate change could torpedo a key element of Mr. Biden’s campaign — and deal untold harm to future generations.

The health of Americans and their climate depends on Democrats passing well-designed, durable programs on which people and businesses can rely. Both sides of the party must keep this in mind as the Democrats pare their legislative ambitions.