Hillary Clinton and Bernie Sanders stand next to each other at the start of the MSNBC Democratic Candidates Debate Feb. 4, in Durham, N.H. Joe Raedle/Getty Images hide caption

toggle caption Joe Raedle/Getty Images

Republican presidential candidate, New Jersey Gov. Chris Christie points toward Republican presidential candidate, Sen. Marco Rubio at the other end of th stage as Republican presidential candidate, retired neurosurgeon Ben Carson looks on during a Republican presidential primary debate hosted by ABC News at the St. Anselm College on Saturday in Manchester, N.H. David Goldman/AP hide caption

toggle caption David Goldman/AP

Democratic presidential candidate Sen. Bernie Sanders, D-Vt., speaks at a rally in the Exeter town hall on Feb. 5, in Exeter, N.H. Andrew Burton/Getty Images hide caption

toggle caption Andrew Burton/Getty Images

Republican presidential candidates, from right, Ohio Gov. John Kasich, former Florida governor Jeb Bush and Sen. Marco Rubio, R-Fla., participate Jan. 28 in a GOP debate in Des Moines, Iowa. Rubio's strong third-place finish in Iowa has given him momentum and more backing from the same establishment Republicans that Bush and Kasich need for their campaigns to survive. Scott Olson/Getty Images hide caption

toggle caption Scott Olson/Getty Images

Donald Trump and Russian President Vladimir Putin have exchanged compliments. In the words of one Putin adviser, "he more carefully listens to so-called 'silent majority' of the American nation, who don't want conflict with Russia." Robert F. Bukaty/AP hide caption

toggle caption Robert F. Bukaty/AP