The deficit fluctuates due to structural economic factors. Protectionism has little to no effect. Qualified economists agree with our interpretation.

Most economists do not see the trade gap as money “lost” to other countries, nor do they worry about trade deficits to a large degree. That’s because trade imbalances are affected by a host of macroeconomic factors, including the relative growth rates of countries, the value of their currencies, and their saving and investment rates. For instance, America’s trade deficit narrowed dramatically during the Great Recession, when national consumption faltered.

Mr. Trump has long argued that the trade deficit hinders economic growth, and that reducing it will accelerate American job creation. Even those who agree with that view say there are better ways to reduce the imbalance than through tariffs, which can backfire and further widen the trade deficit if other countries impose reciprocal tariffs.

“If you look across countries, there’s no evidence that high tariffs reduce your trade deficit,” said Joseph E. Gagnon, a senior fellow at the Peterson Institute for International Economics, and a co-author of a 2017 book of policy recommendations on how to reduce trade imbalances.

“The trade deficit is a terrible metric for judging economic policy,” said Lawrence H. Summers, a Harvard economist and former chairman of President Barack Obama’s National Economic Council. Mr. Summers said tariffs would actually worsen deficits by making American companies that ship steel and aluminum overseas less competitive, and by inviting foreign retaliatory tariffs against other exports.