Which president led the U.S. during the Mexican-American War?

Which president made the Louisiana Purchase in 1803? Which president sent Lewis and Clark on their expedition? Which president issued the doctrine warning Europe against new colonization in the Americas? Which president signed the Indian Removal Act of 1830, leading to the Trail of Tears? Which president issued the Emancipation Proclamation? In what year did Abraham Lincoln deliver the Gettysburg Address? Which Union general became the 18th President? Which president led the "Rough Riders" during the Spanish-American War before becoming president?