By the Treaty of Guadalupe Hidalgo, the United States gained all of present-day California, Nevada, Utah, and New Mexico and parts of Arizona, Colorado, and Wyoming. The Southern boundary of Texas was finally settled. But it was surely one of the most procedurally bizarre treaties the U.S. Senate has ever ratified.

President Polk sent Nicholas Trist, chief clerk of the State Department, to negotiate with the Mexican Government after General Winfield Scott’s successful occupation of Veracruz during the Mexican War. Trist was his own man, however. His initial negotiations committed him to positions that apparently made fidelity to his official instructions impossible. Fed up with Trist’s freewheeling accommodationism and his insufferable vanity, Polk stripped him of all diplomatic credentials and ordered him back home.

On December 4, 1847, Robert Merry tells us, a friend called on Trist to converse about the fate of his mission. Trist confessed a desire to continue negotiating anyway in light of local political developments that Polk and his cabinet would not hear about for quite some time. Trist’s Friend (James Freaner) “practically leaped from his chair” and delivered a most consequential soliloquy:

Mr. Trist, make the Treaty. Make the Treaty, Sir! It is now in your power to do your country a greater service than any living man can render her. . . . You are bound to do it. Instructions or no instructions, you are bound to do it. Your country, Sir, is entitled to this service from you. Do it, Sir!

“I will make the Treaty,” Trist resolved then and there. And he did, as a private citizen who happened to extract from his opposites final terms agreeable to the administration. When Polk got wind of Trist’s game and had a cabinet secretary demand his return once more, Trist recklessly reasoned that the president had no authority to recall him from a position he no longer occupied (“I’m just a dude hanging out in Mexico”). Here are portions of the first and last pages of Trist’s message to Secretary of State James Buchanan that served as a cover letter for a treaty “signed one hour ago at the City of Guadalupe”: Trist asked the very man who convinced him to make the treaty to deliver it to the president who instructed Trist not to make the treaty. Polk despised Trist for his insubordination, but the President swallowed his sanctimony and transmitted the Treaty of Guadalupe Hidalgo to the Senate. Trist correctly calculated that Polk would seize this annoyingly unconventional opportunity for a profitable peace.

I’ll upload more Guadalupe Hidalgo pictures later, but I thought I’d confine this post to the interesting tale of how the treaty came to be. Another neat fact about Trist: he married Thomas Jefferson’s granddaughter Virginia Jefferson Randolph and was at the former president’s bedside when he died on July 4, 1826. Trist’s account is one of the few available to historians seeking to reconstruct Jefferson’s last words.

Edit (11/28/11): I just learned about the Logan Act of 1799, which forbade any American citizen from negotiating with a foreign government merely in his capacity as a private citizen. Trist clearly could have been fined and imprisoned under its terms—one of the largest territorial acquisitions in American history was apparently negotiated criminally.