The two sides are working to reach a budget compromise before June 1, when Treasury Secretary Janet Yellen has said the country could default.

McCarthy and Republicans are insisting on spending cuts in exchange for raising the debt limit. Biden has come to the negotiating table after balking for months but says the GOP lawmakers will have to back off their “extreme positions.”

On Sunday evening, negotiators met again and appeared to be narrowing on a 2024 budget year cap that could resolve the standoff. After speaking with Biden by phone as the president traveled home from a trip to Asia, McCarthy sounded somewhat optimistic. But he warned that “there’s no agreement on anything.”

A look at the negotiations and why they are happening:

What is the debt ceiling fight all about?

Once a routine act by Congress, the vote to raise the debt ceiling allows the Treasury Department to continue borrowing money to pay the nation’s already incurred bills.

The vote in more recent times has been used as a political leverage point, a must-pass bill that can be loaded up with other priorities.

House Republicans, newly empowered in the majority this Congress, are refusing to raise the debt limit unless Biden and the Democrats impose federal spending cuts and restrictions on future spending.

The Republicans say the nation’s debt, now at $31 trillion, is unsustainable. They also want to attach other priorities, including stiffer work requirements on recipients of government cash aid, food stamps and the Medicaid health care program. Many Democrats oppose those requirements.

Biden had insisted on approving the debt ceiling with no strings attached, saying the U.S. always pays its bills and defaulting on debt is non-negotiable.

But facing a deadline as soon as June 1, when Treasury says it will run out of money, Biden launched negotiations with Republicans.

Is it close to being resolved?

There are positive signs, though there have been rocky moments in the talks.

Start-stop negotiations were back on track late Sunday, and all sides appear to be racing toward a deal. Negotiators left the Capitol after 8 p.m. Sunday and said they would keep working.

McCarthy said after his call with Biden that “I think we can solve some of these problems if he understands what we’re looking at.”

The speaker added: “We have to spend less money than we spent last year.”

Biden, for his part, said at a press conference in Japan before departing: “I think that we can reach an agreement.”

But reaching an agreement is only part of the challenge. Any deal will also have to pass the House and Senate with significant bipartisan support. Many expect that buy-in from the White House and GOP leadership will be enough to muscle it over the finish line.

What are the hangups?

Republicans want to roll back spending to 2022 levels and cap future spending for the next decade.

Democrats aren’t willing to go that far to cut federal spending. The White House has instead proposed holding spending flat at the current 2023 levels.

There are also policy priorities under consideration, including steps that could help speed the construction and development of energy projects that both Republicans and some Democrats want.

Democrats have strenuously objected to a Republican push to impose stiffer work requirements on people who receive government aid through food stamps, Medicaid health care and the cash assistance programs.

Biden, though, has kept the door open to some discussion over work requirements.

What happens if they don’t raise the debt ceiling?

A government default would be unprecedented and devastating to the nation’s economy. Yellen and economic experts have said it could be “catastrophic.”

There isn’t really a blueprint for what would happen. But it would have far-reaching effects.

Yellen has said it would destroy jobs and businesses and leave millions of families who rely on federal government payments to “likely go unpaid,” including Social Security beneficiaries, veterans and military families.

More than 8 million people could lose their jobs, government officials estimate. The economy could nosedive into a recession.

“A default could cause widespread suffering as Americans lose the income that they need to get by,” she said. Disruptions to federal government operations would impact “air traffic control and law enforcement, border security and national defense, and food safety.”

Is there a backup plan if talks fail?

Some Democrats have proposed that they could raise the debt ceiling on their own, without help from Republicans.

Progressives have urged Biden to invoke a clause in the Constitution’s 14th Amendment that says the validity of the public debt in the United States “shall not be questioned.” Default, the argument goes, is therefore unconstitutional.

Supporters of unilateral action say Biden already has the authority to effectively nullify the debt limit if Congress won’t raise it, so that the validity of the country’s debt isn’t questioned. The president said Sunday that it’s a “question that I think is unresolved,” as to whether he could act alone, adding he hopes to try to get the judiciary to weigh in on the notion for the future.

In Congress, meanwhile, House Democratic leader Hakeem Jeffries has launched a process that would “discharge” the issue to the House floor and force a vote on raising the debt limit.

It’s a cumbersome legislative procedure, but Jeffries urged House Democrats to sign on to the measure in hopes of gathering the majority needed to trigger a vote.

The challenge for Democrats is that they have only 213 members on their side — five short of the 218 needed for a majority.

Getting five Republicans to cross over and join the effort won’t be easy. Signing onto a “discharge” petition from the minority is seen as a major affront to party leadership, particularly on an issue as important as the debt ceiling. Few Republicans, if any, may be willing to suffer the consequences.