Washington is gearing up for another big fight over whether to raise or suspend the nation’s debt limit, with Treasury Secretary Janet Yellen warning last week that the United States will reach its existing borrowing cap of $31.4 trillion Thursday.

The United States borrows huge sums of money by selling Treasury bonds to investors across the globe and uses those funds to pay existing financial obligations, including military salaries, safety net benefits and interest on the national debt. Once the United States hits the cap, Treasury can use “extraordinary measures” — suspending some investments and exchanging different types of debt — to try to stay beneath the cap for as long as possible. But eventually, the United States will need to either borrow more money to pay its bills or stop making good on its financial obligations, including possibly defaulting on its debt.

What is the debt limit? >> The debt limit is a cap on the total amount of money that the federal government is authorized to borrow to fulfill its financial obligations. Because the United States runs budget deficits — meaning it spends more than it brings in through taxes and other revenue — it must borrow huge sums of money to pay its bills. That includes funding for social safety net programs, interest on the national debt and salaries for troops. The debt ceiling debate often elicits calls by lawmakers to cut back on government spending, but lifting the debt limit does not authorize any new spending and in fact simply allows the United States to finance existing obligations.

When will the debt limit be breached? >> The United States is expected to hit its technical debt limit Thursday. At that point, the Treasury Department will begin using “extraordinary measures” to continue paying the government’s obligations. Those are essentially fiscal accounting tools that curb certain government investments so that the bills continue to be paid.

Those options could be exhausted by June, Yellen told Congress last week. The Bipartisan Policy Center, which closely tracks the debt limit deadline, estimates that the Treasury will really run out of cash — what’s known as the X-date — sometime around the middle of the year.

How much debt does the U.S. have? >> The national debt crossed $31 trillion for the first time last year. The borrowing cap is set at $31.381 trillion.

What happens if the debt limit is not lifted or suspended? >> Once the government exhausts its extraordinary measures and runs out of cash, it would be unable to issue new debt. That means it would not have enough money to pay its bills, including interest and other payments it owes to bondholders, military salaries and benefits to retirees.

Economists and Wall Street analysts warn that such a scenario would be economically devastating and could plunge the globe into a financial crisis.

Can the government do anything to forestall disaster? >> There is no official playbook for what Washington could — or would — do if the U.S. really was unable to pay its bills. But options do exist. The Treasury could try to prioritize payments, such as paying bondholders first.

If the United States does default on its debt, which would rattle the markets, the Federal Reserve could theoretically step in to buy some of those Treasury bonds. That could help calm what would undoubtedly be panic in the Treasury markets and elsewhere.