Sara Burnett/Associated Press

Nikki Haley made a subtle reference to the historic nature of her candidacy as she announced her campaign for the Republican presidential nomination. The former South Carolina governor and U.S. ambassador to the United Nations said in a video that she doesn't put up with bullies. She added that "when you kick back, it hurts them more if you're wearing heels." The introduction captured the balancing act women — particularly conservative women — often navigate as they aspire to win the top job in American politics. They must show toughness to prove they can compete against rivals who are almost always men for a job that has only been held by men.