The 2020 Iowa Democratic Caucuses, a critical early contest on the path to winning the nomination, begin tonight. After that, the pace of the primaries picks up fast, with important contests in New Hampshire, Nevada, and South Carolina. Here's the latest polling of the frontrunners in each of those states. Vermont Senator Bernie Sanders tops polls in Iowa and New Hampshire, but former Vice President Joe Biden is number one in Nevada and has a commanding lead in South Carolina.
