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 of 10,707 adults aged 18 and over, including 9,405 registered voters.

Support for Trump among most demographic groups has remained consistent in this week's tracking poll compared to previous weeks. However, when just looking at Republicans, excluding independents who lean toward the Republican Party, he now enjoys 49 percent support compared to 43 percent last week. This 6-point gain is important, as Trump usually does well among independents, but has struggled to win over more traditional Republicans so far. Support for both John Kasich (15 percent) and Ted Cruz (28 percent) is down among Republicans compared to the past few weeks.