Nicholas P. Trist was a well-connected government employee who had served as a private secretary to Andrew Jackson and married the granddaughter of Thomas Jefferson. During the Polk administration he was appointed chief clerk at the Department of State and in 1847 was dispatched to seek an end to the Mexican War.
Trist, fluent in Spanish, arrived in Mexico in May 1847 and opened negotiations. He managed to secure an armistice following the American victories at Contreras and Churubusco in August. The Polk administration, however, was unhappy with the slow course of events and formally recalled their representative. Trist believed he was inching closer to a final agreement and decided to ignore his summons to Washington. He was supported in that decision by Winfield Scott and his Mexican counterparts.
The document that emerged from the negotiations was basically faithful to the original instructions provided by Polk. Mexico, however, refused to give up Baja California and insisted upon maintaining a strip of land to connect that area with the mainland. The fate of San Diego slowed the talks at one point, but that matter was resolved in favor of the United States.
Although he was angry, Polk was relieved to find a treaty to his liking and urged its ratification by the Senate. Trists independence was not forgiven, however, and nearly 25 years passed before he could collect his pay and expenses from the government.