Nikki Haley, the former governor of South Carolina, is running for president. Vox’s Andrew Prokop says she’s likely the first of many prominent Republicans to challenge Trump. This episode was produced by Miles Bryan, edited by Amina Al-Sadi, fact-checked by Laura Bullard and Matt Collette, engineered by Paul Robert Mounsey, and hosted by Noel King. Transcript at vox.com/todayexplained   Support Today, Explained by making a financial contribution to Vox! bit.ly/givepodcasts Learn more about your ad choices. Visit podcastchoices.com/adchoices