Politicians often use the terms “debt” and “deficit” interchangeably, but they refer to two different figures. The annual budget deficit, which stood at about $587 billion in 2016, is the gap between what the federal government spends and what it collects in tax revenue in a given year. The public debt, as the Treasury Department defines it, is the accumulation of annual deficits—the amount of money the government borrows by selling Treasury securities.

Deficits have gone up and down over the years, but the debt has only gone in one direction—up—and it will continue to do so under the next president, whether it is Clinton or Donald Trump. “Whoever is president will actually be adding $9 trillion to the debt over the next 10 years unless they make changes,” said Maya MacGuineas, president of the Committee for a Responsible Federal Budget, a nonpartisan fiscal watchdog group. “So it won’t be policies that they put in place” that will cause an increase, “but the current trajectory is that we’ll borrow $9 trillion over the next 10 years.” Much of that $9 trillion will come from so-called mandatory spending on programs like Medicare, Medicaid, and Social Security, as well as the 16 percent of the annual budget spent on defense. Neither Clinton nor Trump is proposing to significantly curtail those programs, and Trump has vowed to spend more on defense.

“For a candidate to say they have a plan that wouldn’t add a penny to the debt, they’d actually need a plan to save $9 trillion,” MacGuineas said. “She doesn’t have that, and no one could actually even be expected to have that. We are going to add to the debt.

“What she’s saying in budget-speak is she’s not going to add more to the debt than we are already on track to borrow,” she said.

That’s what Clinton’s campaign says as well. Aides on Thursday said she was simply talking about her “pay-as-you-go” approach to fiscal policy, which they characterized as a middle ground between the austerity budgets proposed by Republicans in Congress and the budget-busting tax cuts that Trump has championed. Still, the clear-cut debt promise is a questionable one from a candidate famous for her attention to detail. For support, her campaign highlighted an analysis of her economic plans by the Committee for a Responsible Federal Budget. Yet even that study found that Clinton’s policies would add $200 billion to the debt over a decade, in large part because she has not specified the business taxes she said she would raise.

Still, Clinton would be on stronger footing if she had used the word “deficit” instead of “debt.” President Obama, for example, can credibly claim to have presided over a sharp reduction in the annual budget deficit even as the national debt has nearly doubled during his tenure. And while the current campaign hasn’t focused on policy, it’s easy to see how Republicans in two or four years could turn Clinton’s pledge not to add a penny to the debt into the next iteration of George H. W. Bush’s “Read my lips: No new taxes,” or Obama’s health-care assurance, “If you like your plan, you can keep it.” The TV ad juxtaposing Clinton’s words and the national debt clock practically writes itself.