Hillary Clinton is planning to launch her presidential candidacy on Sunday through a video message on social media, a person close to her campaign-in-waiting tells CNN, followed immediately by traveling to early-voting states of Iowa and New Hampshire to start making her case to voters. The trip to Iowa, where a third-place finish in 2008 ultimately led to the collapse of her presidential aspirations, illustrates what aides say is a commitment to not take anything for granted in her second bid for the White House, even though she dominates the likely Democratic field in 2016. Clinton has already filmed her...