Susan Walsh / AP
This photo taken Saturday, June 21, 2014, shows demonstrators protesting outside of the White House in Washington against renewed U.S. involvement in Iraq. In charting a new phase of American military engagement in Iraq on Thursday, President Barack Obama pledged that his war-weary country will not be "dragged back" into a lengthy conflict or become ensnarled in "mission creep." But recent U.S. military history is full of warning signs about the difficulty of keeping even a limited mission from expanding and extending.