The South Carolina Democratic primary will determine whether Joe Biden’s campaign stays alive, or whether another candidate can lay claim to being the strongest challenger to national front-runner Bernie Sanders, writes Sahil Kapur of NBC News in an analysis. Here are five things to watch for when polls close at 7 p.m. EST. Click the “Read More” button to read Kapur’s analysis, and download the NBC News app for latest news and analyses on the South Carolina primary. | 