The nineteenth-century historian and legal scholar James Schouler called Polk’s insistence on the Rio Grande as the Texan boundary “pretentious,” and it has found few defenders among historians since. Even Justin Smith, the historian whose book The War with Mexico (1919) remains the account most sympathetic to Polk, recognized that his boundary claim was “unsound.” Polk’s twentieth-century biographer Charles Sellers called his insistence on the Rio Grande boundary “indefensible”—meaning it was logically indefensible.
