A voter wears buttons for Democratic presidential candidates Sen. Bernie Sanders, I-Vt., and Hillary Clinton buttons, March 31, 2016, in New York. (Photo by Mary Altaffer/AP)

Why Clinton's lead over Trump would grow

The latest NBC News/Wall Street Journal poll shows Hillary Clinton with a narrow three-point lead over Donald Trump, 46 percent to 43 percent. But if Bernie Sanders were out of the race the NBC News political unit estimates her lead would likely be much larger, perhaps up around eight points, 51 percent to 43 percent.