Despite Donald Trump leading in the polls, victory in the GOP presidential primaries isn’t certain. Ahead of the Iowa caucuses, Trump hopes to extinguish his opponents. But history has shown that not every winner in Iowa goes on to become the nominee. Read more:Donald Trump has consistently led his opponents in polling for the Republican nomination, often by a wide margin. But victory isn’t certain. In Iowa, the first state in the Republican primaries, Trump wants to fully knock out his competitors, but that may be easier said than done. Support for former U.N ambassador Nikki Haley appears to be growing, and even if Haley loses in Iowa, a strong performance could give her campaign enough momentum to win in New Hampshire later this month. Meryl Kornfield, Michael Scherer and Hannah Knowles join us from the campaign trail to explain everything ahead of the caucuses in Iowa on Monday.