The following editorial appears on Bloomberg View.

For Congress, in a year when voters of both parties are worried about globalization, the political cost of ratifying the Trans-Pacific Partnership trade deal may seem prohibitive. But the economic case for the pact is convincing. And in Southeast Asia, the strategic costs of not approving it are high — and rising fast.

As the world anticipates an international court verdict against China’s expansive maritime claims, tensions in the South China Sea are increasing. China has vowed to defy any adverse ruling. And nervous countries in the region are wondering whether they can count on the U.S. to resist China’s territorial expansionism.

The best way for the U.S. to reassure these nations is to strengthen its commercial ties to the region. After years of hard negotiations and painful compromises all around, the TPP has become the most important test of American commitment to Asia — a “demonstration with substance,” as Singaporean Prime Minister Lee Hsien Loong put it recently.

The deal would bind the U.S. economy more closely with those in the region. It would be a magnet for Thailand, Indonesia and other countries that aren’t yet members. And it would convince Asian nations, far more than words can, that the U.S. has interests in the region it’s willing to defend.

The deal would also boost the U.S. economy, presenting the other signatories with a vibrant source of demand for their goods. And passage of the TPP, in the face of political attacks, would help convince doubters that the U.S. remains capable of constructive cooperation both within Washington and with the world.

A successful trade deal wouldn’t directly set the U.S. and China against each other. One day, in fact, China should be allowed to join the pact. In contrast, the cost of defending U.S. interests in the Pacific with battleships and bombers alone is considerable and probably not sustainable over the long term. Congress should factor that, too, into its political calculations on the TPP.