The warnings about a US debt default are earnest and urgent:

Default would cause a "Social Security shutdown," according to Senate Majority Leader Chuck Schumer.

There would be "economic calamity," according to Treasury Secretary Janet Yellen.

For a Republican prediction, look to the "widespread job losses, decimated retirement savings and higher borrowing costs" anticipated by Joshua Bolten, the CEO of Business Roundtable and the former White House chief of staff under President George W. Bush.

Negotiations between the White House and congressional Republicans just got underway Tuesday with the first in-person debt default meeting between President Joe Biden, House Speaker Kevin McCarthy and other leaders.

Moody's Analytics has predicted a 2008-style crisis, with "spiking interest rates and plunging equity prices," even if it's just a brief breach of the debt limit.

CNN's Tami Luhby and Elisabeth Buchwald have documented these possible outcomes: "5 ways a debt default could affect you."

But for all the warnings, the specifics of when the US will cross the so-called X-date -- when the country could default -- and what will happen in the immediate aftermath are maddeningly vague.

We don't know the X-date

"It is impossible to predict with certainty the exact date when Treasury will be unable to pay the government's bills," Yellen told McCarthy in a letter last week.

She said the X-date could arrive as soon as June 1.

Other estimates, like this one from the Bipartisan Policy Center, suggest the X-date could occur any time between early June and early August.

Uncertainty about the consequences

The specifics of what exactly will happen seem a bit like forecasting a hurricane -- there is a predicted path, but nobody really knows what will happen when the storm makes landfall.

While there have been periodic standoffs over the debt ceiling during past periods of divided government, a default has never occurred.

And it is important to note, as Luhby and Buchwald do, that the government does not simply cease to operate.

"To be clear, a debt default doesn't mean all payments would stop and people would permanently lose out on money they are owed," they write. "Treasury would have the funds to satisfy some obligations, but it's not certain how the agency would handle the disbursements. Much would also depend on how long it takes Congress to address the borrowing cap."

Yellen would have to decide whether to prioritize creditors who own debt or the many people who rely on government money for their paycheck or retirement benefits.

Thus, Schumer's prediction that Social Security would shut down seems unlikely, although payments could be delayed.

More danger in a protracted default

Some of the worst predictions are based on the event that lawmakers do not quickly come together when markets get spooked by the lack of action.

In the scenario of a protracted default, a recession would cost millions of jobs and drive up the unemployment rate, according to a report from the White House Council of Economic Advisers.

One likely effect in any default is that simply having the debt will be more expensive. Confidence in the US paying interest on the debt it sells will be shaken. Rates would likely go up.

The monthly US balance sheet

But in the immediate term, there is a distinct lack of clarity on what the Treasury Department would decide to pay and what it might not.

For an idea of what it's facing, look at the Monthly Treasury Statement, the most recent of which is from March.

Receipts: $313 billion

In March, the government brought in $313 billion in total receipts, including $151 billion from individual income taxes; $133 billion in social insurance and retirement taxes, which includes Social Security payroll taxes; and $11 billion in corporation income taxes, among other sources.

Outlays: $691 billion

In March, the government doled out $115 billion for Medicare, $115 billion to Social Security, $87 billion for income security, $86 billion for health spending, $84 billion for national defense and $67 billion for interest on the debt, among other things.

Those figures vary from month to month, and the $378 billion deficit in March was the second largest in the past year.

How many millions of Americans get a regular check from the government?

A lot of people get money from the government.

There are more than 2 million federal civilian workers, millions of federal contractors and around 1.4 million active-duty military members, plus all of the dependents who rely on them. Delays to their paychecks, if it came to that, would ripple out into the economy.

The number of retirees, disabled workers and others who receive monthly Social Security benefits is much larger, at about 66 million.

More than a third of US households get Social Security payments and, separately, more than a third of households are covered by Medicare, according to census data from 2020. Nearly a quarter of households get federal help with health insurance for either adults or children.

Why not simply raise the debt ceiling?

The current impasse between Republicans and the White House is over spending cuts the GOP wants to enact now that it holds a slim majority in the House. They passed a bill through the House as a sort of opening offer in negotiations.

While the debt ceiling will have to be lifted in the coming months, cuts in the bill Republicans passed would not begin immediately. Instead, they would be implemented with the 2024 fiscal year.

That funding would also get separate votes later this year, so expect additional spending debates. In exchange for the cuts, Republicans are offering an approximately one-year $1.5 trillion debt ceiling hike.

RELATED: 43 Senate Republicans vow to oppose debt ceiling increase without spending cuts

What would Republicans cut?

The GOP spending cut proposal also lacks specifics.

Applying the cuts across the board would reduce spending by an average of 18% over 10 years at every federal agency, according to a New York Times estimate.

But Republicans have said they would not target Social Security, Medicare, veterans or defense spending -- which make up a very large portion of the budget. Applying the equivalent of an across-the-board cut to the remaining federal agencies could result in more than 50% in cuts over 10 years to spending at every agency from Health and Human Services to the Department of Justice.

Biden and Democrats seem unlikely to ever agree to that level of spending cuts. The question is what they will agree to, if anything, and whether any agreement comes before the unknown consequences of a debt default.