Donald Trump has reached 50 percent support from Republicans and Republican-leaners nationally for the first time since the beginning of the NBC News|SurveyMonkey Weekly Election Tracking Poll in late December. This milestone is significant as the 2016 primary heads into its final few weeks of contests, as there has been intense speculation that Trump's support has a ceiling. Though his support has hovered in the high 40s since mid-March, the front-runner had yet to secure half of Republican voters. These results are according to the latest NBC News|SurveyMonkey Weekly Election Tracking poll conducted online from April 18 to April 24...