The Trump administration will soon unveil a “new” North American Free Trade Agreement. U.S. trade negotiators have sought, among other things, to limit its duration, impose new domestic content requirements on certain products, and weaken investor legal protections. Even with these protectionist features, congressional Democrats are unlikely to vote for President Trump’s Nafta 2.0. He will need the support of pro-trade Republicans like me to ensure passage of any new agreement.

To pressure us into voting for an agreement that diminishes free trade, some in the administration suggest offering a grim choice: either approve a diminished Nafta, or the president will unilaterally withdraw the U.S. from the existing Nafta, leaving no Nafta at all.

If presented with this ultimatum, I will vote “no,” urge my colleagues to do likewise, and oppose any effort by the administration to withdraw unilaterally. Pulling out of Nafta by executive fiat would be economically harmful and unconstitutional.

The Framers reserved trade policy for Congress, which has the express authority to establish tariffs and regulate commerce with foreign nations. A president who unilaterally withdrew from Nafta would be directly regulating foreign commerce, imposing significant disruptions on the economy, and infringing on Congress’s status as a coequal branch of government.

There have been instances when presidents have unilaterally terminated treaties. They claimed to be using significant inherent and implied powers on international affairs. But as Justice Anthony Kennedy stated in a 2015 decision, these executive powers aren’t “unbounded.” And none of the handful of treaties that have been terminated unilaterally were principally commercial in nature.