The migration of manufacturing to Mexico could undermine Trump’s promise to voters that ratcheting up tariffs on China would incentivize companies to bring production back to the U.S and give American companies a more even playing field.

US seaports handled the equivalent of 451,000 40-foot containers of goods from China in December, a year-over-year increase of 14.5%.

China has strengthened trade with Latin America at the expense of the U.S. But Donald Trump, who threatens to raise tariffs on Mexico, could upend those ties.