In the early months of Joe Biden’s presidency, the Democrats were something of a big happy family. A slightly dysfunctional one, sure, with dinner table disagreements and that one irksome uncle from West Virginia who can’t stop talking about how much he loves the filibuster. But every family has issues, and the Democrats earlier this year were able to get beyond them to deliver some important policy victories, including Biden’s $1.9 trillion COVID relief bill.

But those familial bonds have been straining recently amid a chaotic, intra-party squabble over a wide-ranging infrastructure plan. The fight, which is fracturing the uneasy alliance progressives and moderates had established to get Biden into office and notch those early wins, has made a tangled mess of a key piece of the president’s domestic agenda—and shrouded the path forward in uncertainty. “I’ve been here for cliffs, and crises and wars. And this is going to be the biggest mash up we’ve ever had since I’ve been here with the debt limit, with the government shutdown, with reconciliation, and with infrastructure, and I have no idea how it all works out,” Democratic Representative Peter DeFazio told Punchbowl News. “No idea. That’s it.”

The issues Democrats are scrambling to resolve are, to some extent, nothing new. Bold progressive priorities, addressing everything from healthcare to education to the climate crisis, are butting up against the ambivalence of party moderates and conservatives, as well as their deference to longstanding but perhaps outdated Senate traditions: the filibuster, which Joe Manchin and Kyrsten Sinema refuse to abolish or reform, and the Senate parliamentarian, who on Sunday ruled that Democrats could not include immigration reform in their reconciliation bill. But it isn’t just the impasse and high-stakes; it’s that this drama is playing out against the backdrop of a debt limit fight with Republicans and a looming government shutdown. The Biden administration insists that there has been progress in the negotiations. But for the Democrats trying to run the gauntlet here, there is a tremendous sense of uncertainty—and fear that a failure to align won’t just derail Biden’s agenda, but that members will “pay for it at the polls.” “If any member of Congress is not concerned that this could fall apart, they need treatment,” Democratic Representative Emanuel Cleaver told Politico.

For House Speaker Nancy Pelosi and Senate Majority Leader Chuck Schumer, who command thin majorities in their chambers, the challenge will be to quickly unite a party that can ill-afford any defections. In the House, progressives like Pramila Jayapal are threatening to blow up the Senate’s more moderate infrastructure bill if there is no guarantee that the more expansive social infrastructure plan will pass. But Manchin and Sinema have balked at that plan and want it scaled back; the conservative West Virginia Democrat has even reportedly suggested delaying action on the ambitious $3.5 trillion deal until next year. Being an election year, that could doom its chances. Manchin has been a frustrating presence in the party throughout Biden’s tenure, having staked out a post as the ultimate gatekeeper for the administration’s agenda. But irritation with the way he has wielded that power may be starting to reach a fever pitch. “I am very tired of it,” Democratic Representative Jamaal Bowman told Politico, referring to Manchin and Sinema. “I don’t think they are making their decisions based on the needs of the American or even the people in their own state.”

What is particularly aggravating here, perhaps, is that Biden’s social infrastructure agenda appears quite popular among the American people. Democratic divisions, which seemed less stark when they were uniting against their common enemy in Donald Trump, are threatening to thwart policies that much of the country actually supports—unless they can get their house in order. “I wish that we could all be more on the same page, in terms of timing, of the need to push the [American Families Plan],” Senator Mazie Hirono told Politico. “I’m hopeful we are going to have a meeting of the minds and not wait until next year … we better have a Plan B.”

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