The next few weeks will be the most challenging in perhaps a decade for Democrats in Congress. They need to figure out a way to keep the government open, raise the debt ceiling to avoid an economic catastrophe, pass emergency natural disaster aid and provide money for resettling Afghan refugees. And that’s just their must-do list.

What Democrats really want to do is write and pass a massive spending bill that dramatically expands the federal government safety net. They also want to send a bipartisan infrastructure bill to President Biden’s desk, and they are trying to pass voting-rights legislation to counter GOP-led efforts at the state level to restrict how people vote, but that could require a historic rules change in the Senate.

Let’s review what Democrats — who are the ones in charge because they have majorities in both chambers — have to do this fall and where the roadblocks are.

What must be done and why

Fund the government: The government’s fiscal year ends Sept. 30, and it’s Congress’s job to fund the government for another year. Congress usually doesn’t pass all its appropriation bills in time, so to avoid a government shutdown, it can and probably will pass a short-term spending bill — known as a continuing resolution — that funds the government at last year’s levels.

Raise the debt ceiling: When the Treasury Department needs to borrow more money to pay its debts, it has to ask Congress for permission. Treasury Secretary Janet Yellen says Congress will need to raise its debt ceiling in October, or the United States could go into default.

Pass emergency disaster aid legislation: At the beginning of September, the White House added another item to Congress’s to-do list: Approve tens of billions of dollars to deal with wildfire, hurricane and flood disasters across the country, plus billions to help resettle Afghan refugees.

What else Democrats are trying to do

Pass a bipartisan infrastructure bill: A bill to work on the nation’s roads, bridges, pipelines and broadband passed the Senate, with the support of 19 Republicans, and there’s an agreement to vote on it this month in the House.

Pass a massive social safety net bill: This is the big one for Democrats. This summer, they approved the outlines of a $3.5 trillion bill that would create universal pre-K, provide free community college and expand Medicare, among its many provisions. No Republicans voted with them on this one. It could be one of the biggest pieces of legislation ever. Now they need to determine the policy details and write legislation laying out exactly what they want to spend that money on and vote on it again. They’re trying to get that done by the end of this month, but lawmakers are starting to say this could drag on for weeks longer than they want.

Pass a voting rights bill: Democrats are running out of time to create a national standard for how people vote. This is in response to Republican-led states that are restricting voting rights in ways that particularly target voters of color and a redistricting cycle in which Republicans can gerrymander their way back into power in the House of Representatives. Senate Democrats have a compromise bill that all 50 members of their caucus support, but it will almost certainly face a Republican filibuster, meaning they have to decide whether they want to tweak or overhaul or even get rid of the filibuster.

Why Democrats are doing much of this alone

Democrats have only a slim majority in Congress, and it’s a very partisan Congress at that. Plus, in the Senate, Republicans can filibuster legislation and require Democrats to secure at least 10 Republican votes to get over that filibuster. We’re expecting such a filibuster on those must-do’s — funding the government and raising the debt ceiling. Sen. Ted Cruz (R-Texas) said he’ll filibuster raising the debt ceiling.

But Senate Minority Leader Mitch McConnell (R-Ky.) has repeatedly said Senate Republicans won’t vote to raise the debt ceiling. He’s playing a daring game of brinkmanship that could mean Congress doesn’t have the votes to raise it, period. And that could mean the government defaults on its loans.

Democrats don’t expect any GOP votes for their $3.5 trillion spending plan. The only way they’re getting this done is to go around Republicans and pass this massive bill through a process called reconciliation. Reconciliation lets Congress pass bills directly related to spending with a simple majority of votes — the minority cannot block these bills with a filibuster.

Passing legislation with only one party might sound easier than having to compromise with the other. But mathematically, it means Democrats have fewer votes to work with to get their big legislative priorities done. And that means any one senator or a handful of Democrats in the House of Representatives could block this.

What could go wrong for Democrats

Let us count the ways.

So much is riding on their ability to pass these bills this fall — there are big economic and political consequences. If there’s a shutdown or the government defaults on its debts because Congress could not raise the debt ceiling, it will be happening while Democrats are in charge of Washington.

Molly Reynolds, a Brookings Institution analyst of congressional budgets, said a government shutdown isn’t out of the question. In the Senate, just one lawmaker can put his or her foot down on an issue by filibustering and gumming up the process. With Congress debating so much, that could happen with any number of issues. (Republican Sen. Rand Paul of Kentucky did this a few years ago over objections about spending, and the government briefly shut down overnight.)

And Democrats have very little margin for error among themselves to pass that huge social safety net legislation. The Senate is split 50-50, and House Democrats have only a handful of votes to spare.

Getting everyone on the same page on a bill this big is going to be tricky. Moderate Democrats such as Sens. Joe Manchin III of West Virginia and Kyrsten Sinema of Arizona want the $3.5 trillion bill to be significantly smaller, potentially by as much as half.

And moderate House lawmakers also are worried about passing something they don’t have an ability to pay for. “The money is just not there,” one Democratic lawmaker told The Washington Post’s Tony Romm.

These lawmakers are backed by outside groups that are worried about how much this bill could add to the federal debt. “I think it’s very concerning they may well not end up paying for it,” said Maya MacGuineas, president of the nonpartisan Committee for a Responsible Federal Budget. “The scale of this is truly massive,” she added.

But liberals in the House — a significant and growing faction — are demanding that Congress spend $3.5 trillion and not a penny less. “There is no flexibility on the price tag, and it’s not because I care about what the top line is,” Rep. Pramila Jayapal (D-Wash.), who leads the roughly 100-member strong Congressional Progressive Caucus, told Romm. “It’s because I care about delivering on these benefits.”

Liberals want to know what the moderates in their party would cut from this package. It’s a good question. Expensive proposals in the legislation such as the child-care tax credit, paid family leave and Medicare expansion are quite popular with voters.

The underlying dynamic is that this may be the Democrats’ first and last chance to make a big mark before they lose power in Washington. Democrats can dodge a Senate Republican filibuster only once or twice for legislation, and then they will be facing the 2022 midterm elections, in which their majorities in both chambers are at risk. It’s possible that Biden finishes his first term with a divided or fully Republican-controlled Congress.

What could go wrong for Republicans

The pressure isn’t just on Democrats. Republicans need to navigate political risks, too.

The firmest line they have drawn is that they won’t help Democrats raise the debt ceiling. “Do you guys think I’m bluffing?” McConnell told Punchbowl News recently. But what happens if Democrats fold that vote into a broader bill to fund the government and approve natural disaster aid to help many Republican states as well? Would Republicans vote against that?

“Ultimately, I think the financial interests that would be badly harmed by a default and that are very supportive of the Republican Party would not tolerate that,” said David Super, a federal budget expert at Georgetown Law.

In addition, surveys indicate that, for now, Democrats’ proposals in their $3.5 trillion social safety net bill are generally popular with Americans. Republicans have tried out various lines of attack on this — it will add to inflation, Democrats are the party of too-big government — but it’s possible that nothing sticks, and they lose this policy battle.

“The fact we haven’t seen a concerted, substantive attack on this,” Super said, “tells me that Republicans are somewhat divided on what’s a good attack and what’s not.”