Trade ministers from the 12 Trans-Pacific Partnership (TPP) member countries participate in a news conference in Atlanta last year. (Erik S. Lesser/European Pressphoto Agency)

HOPE SPRINGS eternal. On that basis, the Obama administration continues to urge congressional approval of the Trans-Pacific Partnership (TPP) as soon as practicable, which would mean after the election and before the end of President Obama’s term. We hope Congress agrees, but candor and realism require us to acknowledge that the prospect is increasingly remote. The far likelier outcome is that the 12-nation , tariff-slashing pact will languish indefinitely. Over the course of a turbulent political year, the American political center has shifted, not only against the TPP but also against trade-expanding multilateral agreements generally.

Therefore, it is not too early to challenge critics of the existing free-trade paradigm: What is your alternative? To be sure, that is an easy question for America Firsters, such as Republican presidential nominee Donald Trump, who believe, simplistically, that global economics is a zero-sum business and that the task is to snatch back, through various protectionist measures, the jobs China, Mexico and other trading partners “stole.” For Mr. Trump’s opponent, Democrat Hillary Clinton, the issue is, or should be, more difficult. After all, she formerly accepted the rationale for the TPP until changing her position under pressure from Sen. Bernie Sanders (I-Vt.). And that rationale was rooted not only in a perception of the U.S. national economic interest but also in an assessment of the U.S. national security interest.

The latter point is important, but, in a political debate understandably focused on the domestic economic impact of trade, too often overlooked. Since the early years after World War II, when the United States helped launch the General Agreement on Tariffs and Trade, expanding global commerce has played a strong supporting role in U.S. strategy. Ever-freer trade, and the ever thickening web of rules-based relationships that it creates, was thought of, correctly, as a “soft power” complement to American military and political clout. Though mutually advantageous economically, the TPP was most important strategically, as an instrument of the Obama administration “pivot” to Asia, in that it would firm up ties among the United States, Japan and — eventually — a bloc of smaller nations, all of which shared the goal of peacefully curbing Chinese plans to dominate the region according to its authoritarian, mercantilist norms.

If the TPP is out, some other institution will have to serve this function. Admittedly, it’s a predicament that advocates of trade expansion with China, President Bill Clinton foremost among them, did not foresee. To the contrary, the consensus at the time of China’s joining the World Trade Organization on Mr. Clinton’s watch was that access to Western markets would induce the Beijing regime to moderate its ambitions and behavior and move toward an open, rules-based economy. Lesson learned. And all the more reason to maintain a robust U.S. commitment to a vital region of the world, where threats to democracy and prosperity include not only Chinese provocations but also North Korean bellicosity and the errant leadership of Philippine President Rodrigo Duterte. The TPP was to be the anchor, symbolic and substantive, of a reinvigorated U.S. presence. The next president cannot simply leave a strategic vacuum in its place.