This is the stance of an increasing number of economists, including prominent voices like Lawrence Summers and Douglas Elmendorf: The United States needs to borrow money and invest it in growing the economy.

We’re also not in danger of being unable to pay back what we owe. The cost of paying interest on the government’s debt is at a 50-year low, consuming just 6 percent of the federal budget.

There would be, at some point, good reason to bring down the debt. A high federal debt load could eventually accelerate inflation, but inflation is all but nonexistent right now. Or the country could find itself in a position where it can’t borrow more money to respond to increasing financial need during an economic downturn. But low interest rates and willing lenders give us plenty of room today.

It’s particularly disappointing that Mrs. Clinton is tying her promise not to add to the debt directly to her infrastructure plan, which offers perhaps the best bang for a government-borrowed buck. That becomes even more important if the economy careens into a ditch again, which some experts think we are due for soon. The best thing she could do would be to put forward a stimulus package with significant spending on building projects — and she would need to finance it by adding plenty of pennies to the debt.

The things that actually drive federal debt into dangerous territory are not the kinds of programs Mrs. Clinton wants to enact. The dangerous trends are the growth in costs related to health care and a retiring baby boom generation. The country’s debt load could be accelerated by a government spending bonanza that doesn’t lead to much growth — say, perhaps, a huge tax cut giveaway to the wealthiest Americans, like the nearly $10 trillion plan Donald J. Trump has put forward and which history has found probably won’t spur the economy.

Mrs. Clinton’s promise is also one that’s not likely to come true. Her policy agenda, if enacted, would be mostly paid for, but would still increase the national debt at about the same rate as is now projected.

This isn’t the first time Mrs. Clinton has made a promise that might sound good to voters but hamstrings her if she takes office. She has been consistently pledging not to raise taxes on those who make less than $250,000, people she calls “middle class” even though median income is more like $54,000. That sounds good to those who already feel financially pinched. But it precludes enacting any programs that increase taxes on people in this category, no matter how small the increase or how much the middle class would actually benefit.

A better promise than Mrs. Clinton’s no-debt vow would be something like this: “I will not significantly run up the national debt to pay for projects that won’t make the economy grow.” That’s more honest and more sound, and it would leave her free to make necessary policy decisions in the White House. But it’s not as neat a slogan, and that makes it a much harder sell.