For months, Sen. Joe Manchin’s refusal to sign onto President Joe Biden’s signature Build Back Better bill has subjected the West Virginia Democrat to substantial flak from party progressives.

But Manchin is hardly the only one responsible for the impasse that threatens to sink Biden’s top legislative priority. Democratic progressives, the Biden White House and party leaders have been unrealistic on how much spending could pass the narrowly divided Congress.

Criticism of Manchin exploded after the West Virginia senator said on Fox News Sunday that he won’t support the current version of the budget reconciliation measure’s massive package of environmental and social proposals.

“He’s going to have a lot of explaining to do to the people of West Virginia,” declared Vermont Sen. Bernie Sanders on CNN’s State of the Union, ignoring the fact that Manchin is more popular there than Biden.

And the White House, in an extraordinary statement from Press Secretary Jen Psaki, accused Manchin of “a sudden and inexplicable reversal in his position,” saying that just days earlier he handed Biden a written outline “that was the same size and scope as the President’s framework.”

Manchin has been inconsistent publicly on which parts of the bill he favors — and precisely how much spending he’d accept. He maintained Sunday his ceiling was always $1.5 trillion, some $600 billion less than the House-passed bill.

But leaders of the Democratic party’s left wing and the White House can’t escape some responsibility for the impasse.

They have endangered BBB’s prospects by unrealistically demanding more spending than can pass a 50-50 Senate where administration legislation needs the votes of the two independently minded Democratic moderates, Manchin and Arizona’s Kyrsten Sinema. In a sense, Sanders exemplifies the problem. Elevated through seniority to lead the Senate Budget Committee, the twice-defeated presidential candidate initially proposed a $6 trillion budget. Later, Sanders suggested a $3.5 trillion “compromise” — still far too large.

Sanders also proposed expanding Medicare to include vision, dental and hearing coverage, an expensive plan primarily benefiting middle- and upper-income recipients. Top House Democrats preferred to expand Obamacare subsidies and extend Medicaid coverage to the poor in states like Texas and Florda.

In retrospect, it’s evident Biden and Speaker Nancy Pelosi stuck too long with Sanders’ $3.5 trillion total, though possibly because they feared House progressives would torpedo a smaller package.

Now, progressives like Sanders are demanding an immediate Senate vote, presumably to embarrass Manchin. Majority Leader Chuck Schumer says the Senate will vote early next year on “a revised version” of the House bill. If the goal is to pass BBB, those revisions better meet some of Manchin’s demands.

After all, this remains the best chance for Democrats to enact popular portions of their social agenda, like universal pre-kindergarten, added day care support, Medicaid expansion, expanded Obamacare subsidies and a range of environmental measures.

Manchin, who says he is open to further talks, signaled an alternate approach by noting how much BBB’s potential long-term cost exceeds its current price tag. He criticized progressives for starting multiple new programs for a few years on the assumption their popularity would force Congress to extend them.

Manchin favors fewer programs, fully funded for the bill’s full 10-year extent; The Washington Post says they include universal pre-kindergarten, Obamacare subsidies, and environmental measures.

This week’s acrimony increases the uncertainty over whether the Democrats can take advantage of their current control of Congress and the White House.

Carl P. Leubsdorf is the former Washington bureau chief of the Dallas Morning News.