In the White House now was James Polk, a Democrat, an expansionist, who, on the night of his inauguration, confided to his Secretary of the Navy that one of his main objectives was the acquisition of California. His order to General Taylor to move troops to the Rio Grande was a challenge to the Mexicans. It was not at all clear that the Rio Grande was the southern boundary of Texas, although Texas had forced the defeated Mexican general Santa Anna to say so when he was a prisoner. The traditional border between Texas and Mexico had been the Nueces River, about 150 miles to the north, and both Mexico and the United States had recognized that as the border. However, Polk, encouraging the Texans to accept annexation, had assured them he would uphold their claims to the Rio Grande. Ordering troops to the Rio Grande, into territory inhabited by Mexicans, was clearly a provocation.