Unfortunately, these benefits are counterbalanced by the Trump administration’s heavy-handed efforts to revive American manufacturing by reducing foreign competition.

The administration used the threat of ending NAFTA to extract agreement from Canada, and especially Mexico, on a package of protectionist measures designed to repatriate jobs in auto manufacturing and associated industries, like steel making. The rules, for example, require that a minimum portion of the average vehicle is produced by workers making at least $16 an hour — far above wage rates in Mexico.

The United States International Trade Commission predicts the measures will succeed in the narrow purpose of shifting work to the United States, but only at a high cost: Consumers will pay more for new vehicles, resulting in fewer sales, and economic growth will suffer.

There is a broader threat, too. Shifting work to Mexico has allowed American car companies to reduce costs, and to compete more effectively with foreign producers. Without NAFTA, there might be even fewer car-making jobs in the United States today. And as a result of the changes, there may be fewer in the future.

The commission still concluded that the new NAFTA would add $68.2 billion to economic output, an increase of 0.35 percent. But its analysis rests on a pair of big assumptions. First, the commission asserted the deal would encourage cross-border investment by easing doubts about the stability of regional trade rules. But one feature of the new deal is an agreement allowing the United States to withdraw after 16 years, which seems likely to have the opposite effect. The commission also projects a big increase in e-commerce, because the deal brings the NAFTA framework into the digital age. But Mexico and Canada already have separately adopted the changes required by the deal.

Finally, the new deal amounts to yet another missed opportunity to forge the international cooperation necessary to limit climate change. More than 100 House Democrats signed a letter earlier this fall seeking binding commitments on climate standards as part of any revisions to NAFTA. But faced with the Trump administration’s willful refusal to address climate change, Democratic leaders decided to prioritize reaching a deal on other issues.

The White House has described the result as “the biggest and best trade deal in the history of the world.” It is more accurately described as a minor deal that may do more harm than good. That it may also be the best possible outcome under current management is a reminder of the many ways in which Mr. Trump’s presidency continues to ill serve the American people.