Sometime in the next two years, the federal debt will likely cross a worrisome threshold: It will exceed the size of the country’s annual economic output (or G.D.P.) for the first time since 1946.

The debt-to-G.D.P. ratio is merely a statistic, and nothing will inherently change when the ratio exceeds 100 percent. But it will be a sign of the country’s serious budget challenges. The large debts of the 1940s had a clear rationale: They were the price of winning a world war against a murderous fascist alliance. Today’s debt has no such simple explanation.

It instead reflects an accumulation of causes, including large tax cuts signed by Republican presidents, the continued rise in spending on Medicare and Social Security as the country ages and stimulus bills passed by both parties during the Covid pandemic and 2007-9 financial crisis. (Spending on the military, by contrast, has declined as a share of G.D.P. in recent years.)

What these causes have in common is a federal government that seems incapable of paying its own bills — and an electorate that tells pollsters it cares about the federal debt but votes for politicians who support low taxes and high spending.

How bad?

Yesterday, the Committee for a Responsible Federal Budget — a group that favors deficit reduction — released a detailed analysis of both Trump’s and Kamala Harris’s economic plans. The group acknowledged the uncertainty about the effects of those plans. Both candidates have been vague about parts of their agendas, and the economy’s performance will also have a big impact on the debt.