The debt ceiling limits the amount of debt that the U.S. Treasury can issue.

Raising the debt ceiling allows Congress to pay for things that it has already decided to spend on. It does not approve new spending. Around one-third of federal spending is discretionary, for which Congress approves annual spending bills with specific instructions about how to spend the money. The other two-thirds is mandatory, meaning money is spent on certain programs established by existing law, such as Medicare, Medicaid and Social Security.

The debt ceiling has become a difficult vote for lawmakers because it’s viewed as one way to force fiscal restraint. If your bank doesn’t increase your credit card limit, the thinking goes, you’re going to have to cut back on spending.

Many economists and investors say that’s a flawed analogy because Congress has already voted to approve the spending. In that sense, refusing to raise the debt limit is a bit like dining and dashing out at a restaurant. Congress knew the bill was coming when it ordered the meal. Refusing to raise the debt limit is like running out of the restaurant before paying the check.