IN FEBRUARY 28, 1848, President James K. Polk received a visit from Ambrose Sevier of Arkansas, chairman of the Senate Foreign Relations Committee, bearing bad news. His committee had just voted to recommend that the full Senate reject a peace treaty that had been painstakingly negotiated between the United States and Mexico.

The news struck Polk hard. Senate ratification would bring an end to a war that had dragged on for two years, cost the country nearly 14,000 lives, generated much venomous recrimination, and sapped Polk's own political standing and that of his Democratic Party. Rejection would mean more bloodshed in Mexico and more bitterness at home, not to mention the dreaded possibility that the United States would have to end the war by conquering more territory and subduing even more Mexican citizens.

Polk was particularly stung when he heard that the committee wanted him to send a proper delegation to Mexico to negotiate a treaty much like the one now before the Senate. The terms of the treaty weren't the problem; it was that it had been negotiated by Nicholas Trist after he had been dismissed from his diplomatic post by Polk.

Polk had felt the same way when he first learned how Trist had defied his recall and seized what he considered a rare and perishable opportunity to deal with the peace faction, which had seized control of Mexico's reeling government.

If bellicose anti-American factions took over, Trist surmised, the chance for peace would be lost.

Polk curbed his anger when he saw that Trist's treaty conformed to presidential instructions. Besides, the president foresaw disaster looming if this opportunity evaporated. As he told his cabinet, the United States would never obtain better terms. If these terms were now rejected by the United States and hostilities resumed, the antiwar House would probably shut off authorization for troops and money. He might have to withdraw U.S. forces simply for their own protection, and the vast conquered territory—California and a huge swath of southwestern land—could be gone forever. In short, said the president, to reject the treaty could render it impossible "for my administration to be sustained." So he had sent it to the Senate, only to hear now that Foreign Relations Committee members were toying with blocking this fragile opportunity for peace.

There was no doubt in anyone's mind that the war with Mexico was Polk's war, which he had engineered following the U.S. annexation of Texas. Texas—and Polk—deemed that its territory extended to the Rio Grande, while Mexico held that the proper boundary was the Nueces River, some 200 miles to the east. Polk had sent an army to the east bank of the Rio Grande, which had promptly come under attack by Mexican troops, just as Polk had anticipated. And so he got his war.

Militarily, it had yielded a stunning record of U.S. triumph. Polk's generals never lost a battle, conquering vast provinces that, if retained, would render the United States one of the largest nations of the globe. An expeditionary force