President Trump’s protectionist impulses have upended the global debate about international trade.

But so far, his policies have barely changed a fundamental reality: The United States is still less protectionist than it has been throughout most of its history or than most nations are today.

Even if the tariffs currently in place inflict only limited damage on the economy, however, the consequences will be much more severe if Mr. Trump follows through on his threats to take much more aggressive action.

Here’s the big picture.

The average tariff rate in the United States was 1.4 percent, according to the latest data compiled by the United States International Trade Commission. That was nearly as low as it has ever been.

But that figure only includes tariffs imposed in the administration’s first year. A lot has happened since then.