In a letter to congressional leadership on Friday, Treasury Secretary Janet Yellen gave negotiators on the debt limit some much-needed breathing room, pushing back the 'x-date' -- the day when the country can no longer fulfill its obligations -- to June 5. The previous x-date, by Yellen's estimation, was June 1.

Yellen's warning of a default, which experts warn could result in a global financial catastrophe, comes as President Joe Biden and House Speaker Kevin McCarthy, R-Calif., are expressing optimism that they are in the home stretch on a deal to raise the country's borrowing power.

"It's very close," Biden told reporters Friday night.

"Based on the most recent available data, we now estimate that Treasury will have insufficient resources to satisfy the government’s obligations if Congress has not raised or suspended the debt limit by June 5," Yellen wrote in a letter to congressional leadership, urging lawmakers to take action quickly.

"We have learned from past debt limit impasses that waiting until the last minute to suspend or increase the debt limit can cause serious harm to business and consumer confidence, raise short-term borrowing costs for taxpayers, and negatively impact the credit rating of the United States," Yellen wrote. "In fact, we have already seen Treasury’s borrowing costs increase substantially for securities maturing in early June.

"If Congress fails to increase the debt limit, it would cause severe hardship to American families, harm our global leadership position, and raise questions about our ability to defend our national security interests," she added.

Before heading to Camp David on Friday, President Biden said that "things are looking good" with the state of the debt limit negotiations.

"I'm very optimistic," Biden told reporters, adding: "I'm hopeful we'll know by tonight whether we are going to be able to have a deal."

Negotiators in McCarthy's camp agreed with Biden's optimism that they were close to a deal. North Carolina Rep. Patrick McHenry, one of McCarthy's top GOP negotiators, told reporters on Friday, told reporters that he "concurs" with the White House's assessment, but did not offer a timeline about when a deal might be struck.

"We have to make sure we are aligned on text, aligned on an agreement," he advised reporters later Friday. "There’s significant challenges here and I don’t know if that’s hours or days."

"I’m Catholic and everybody wants to look for the white smoke," he quipped. "We’re not at that stage yet."

"I thought we made progress last night," McCarthy told reporters earlier on Friday. We've got to make more progress."

"I'm gonna work as hard as we can to try to get this done, get more progress today and finish the job," he said, adding: "I'm a total optimist."

Biden and Republican House Speaker Kevin McCarthy have seemed to be narrowing on a two-year budget-slashing deal that would also extend the debt limit into 2025 past the next presidential election. After frustrating rounds of closed-door talks, a compromise had appeared to be nearing on Friday.

Republicans have made some headway in their drive for steep spending cuts that Democrats oppose. However, the sides are particularly “dug in” over McCarthy’s demands for tougher work requirements on government food stamp recipients that Democrats say is a nonstarter.

Earlier Friday, McCarthy said his Republican debt negotiators and the White House had hit “crunch” time, straining to wrap up an agreement with Biden as lawmakers broke for the long Memorial Day holiday weekend.

When asked if a deal was possible Friday, McCarthy reiterated: "I'm gonna work as hard as I can. As soon as we get a deal, we're gonna get a deal but it has to be worthy of the American people."

Any deal would need to be a political compromise, with support from both Democrats and Republicans to pass the divided Congress. Failure to lift the borrowing limit, now $31 trillion, to pay the nation’s incurred bills, would send shockwaves through the U.S. and global economy.

But many of the hard-right Trump-aligned Republicans in Congress have long been skeptical of Treasury’s projections, and they are pressing McCarthy to hold out.

At an event earlier Friday celebrating the NCAA championship-winning LSU women's basketball team, Biden gave a shoutout to one of this top negotiators -- Office of Management and Budget Director Shalanda Young, a Louisiana native -- saying she’s “putting together a deal, hopefully.”

While the contours of the deal have been taking shape to cut spending for 2024 and impose a 1% cap on spending growth for 2025, the two sides remain stuck on various provisions. The debt ceiling, now at $31 trillion, would be lifted for two years to pay the nation’s incurred bills.

A person familiar with the talks said the two sides were “dug in” on whether or not to agree to Republican demands to impose stiffer work requirements on people who receive government food stamps, cash assistance and health care aid.

House Democrats have called such requirements for health care and food aid a nonstarter.

Asked if Republicans would relent on work requirements, Louisiana Rep. Gareet Graves, McCarthy's other top lieutenant in the negotiations, fumed: “Hell no, not a chance.”

House Republicans had pushed the issue to the brink, displaying risky political bravado in leaving town for the Memorial Day holiday. Lawmakers are tentatively not expected back at work until Tuesday, but now their return is uncertain.

“The world is watching,” said International Monetary Fund Managing Director Kristalina Georgieva after meeting Friday with Yellen. “Let’s remember we are now in the 12th hour.”

Weeks of negotiations between Republicans and the White House have failed to produce a deal — in part because the Biden administration resisted negotiating with McCarthy over the debt limit, arguing that the country’s full faith and credit should not be used as leverage to extract other partisan priorities.

“We have to spend less than we spent last year. That is the starting point,” said McCarthy.

One idea is to set the topline budget numbers but then add a “snap-back” provision to enforce cuts if Congress is unable during its annual appropriations process to meet the new goals.

On work requirements for aid recipients, the White House is particularly resisting measures that could drive more people into poverty or take their health care, said the person familiar with the talks, who was granted anonymity to describe behind-closed-door discussions.

Over the Republican demand to rescind money for the Internal Revenue Service, it’s still an “open issue” whether the sides will compromise by allowing the funding to be pushed into other domestic programs, the person said.

In one potential development, Republicans may be easing their demand to boost defense spending beyond what Biden had proposed in his budget, instead offering to keep it at his proposed levels, according to another person familiar with the talks.

The teams are also eyeing a proposal to boost energy transmission line development from Sen. John Hickenlooper, D-Colo., to facilitate the buildout of an interregional power grid.

Meanwhile, McCarthy is feeling pressure from the House’s right flank not to give in to any deal, even if it means blowing past the Treasury deadline.

McCarthy said Donald Trump, the former president who is again running for office, told him, “Make sure you get a good agreement.”

Watchful Democrats, though, are also pressing Biden. The top three House Democratic leaders led by Rep. Hakeem Jeffries spoke late Thursday with the White House.

McCarthy has promised lawmakers he will abide by the rule to post any bill for 72 hours before voting. The Democratic-held Senate has vowed to move quickly to send the package to Biden’s desk, right before next Thursday’s possible deadline.

Meanwhile, Fitch Ratings agency placed the United States’ AAA credit on “ratings watch negative,” warning of a possible downgrade.

The White House has continued to argue that deficits can be reduced by ending tax breaks for wealthier households and some corporations, but McCarthy said he told the president as early as their February meeting that raising revenue from tax hikes was off the table.

While Biden has ruled out, for now, invoking the 14th Amendment to raise the debt limit on his own, Democrats in the House announced they have all signed on to a legislative “discharge” process that would force a debt ceiling vote. But they need five Republicans to break with their party and tip the majority to set the plan forward.

They are all but certain to claw back some $30 billion in unspent COVID-19 funds now that the pandemic emergency has officially been lifted.