Trump’s Tax Plan Could Add Trillions in Debt. Harris’s Is a Mystery.

Former President Donald J. Trump keeps adding new tax cuts to his list of campaign promises, and their projected costs keep piling up.

Independent analyses suggest Mr. Trump’s plans could add close to $4 trillion over the next decade to America’s already fast-growing national debt, even after factoring in additional revenues from new taxes he wants to impose on imports.

It is impossible to make a similar estimate for Vice President Kamala Harris, Mr. Trump’s Democratic opponent this fall. She has not laid out any tax or spending plans, or other economic policy proposals, with enough detail to estimate whether they would add to deficits or reduce them.

Total federal debt is now about $35 trillion, up from about $20 trillion when Mr. Trump took office in 2017, Treasury Department data shows. It grew by about $7.8 trillion on Mr. Trump’s watch and has increased by about $7.3 trillion on President Biden’s watch thus far.

Deficit hawks in Washington warn that a further acceleration would elevate risks of an economically debilitating spiral, where rising debt pushes up borrowing costs in financial markets. That would then cause the debt to further balloon.

“It’s a lot more troubling now, because the overall fiscal and economic environment is a lot worse” than it was before Mr. Trump and Mr. Biden took office, said Marc Goldwein, the senior vice president for the nonpartisan Committee for a Responsible Federal Budget in Washington.