While Trump has had the nomination locked down for weeks, he has now reached the threshold of 1,237 delegates with the help of previously uncommitted delegates who now support his candidacy. A handful of states, including the large prizes of California and New Jersey, will hold the final primaries on June 7.
While Trump will not formally accept the party's nomination until the delegates cast their votes on the convention floor in July, crossing the threshold effectively puts to rest any remaining suspense about the possibility of a messy and contested convention. For months, drama and tumult have rocked the Republican Party, as a fervent anti-Trump movement launched a full-on onslaught to derail his candidacy.
But the flurry of "Never Trump" activities, including a slew of negative ads against Trump and efforts to draft a third-party candidate, ultimately proved unsuccessful.
Speaking at a news conference in Bismarck, North Dakota, Trump reveled in the fact that he had clinched his party's nomination before Hillary Clinton.
The launch of his unlikely presidential campaign last summer was met with widespread ridicule. His wholly unorthodox campaign and rhetoric not only unsettled and alarmed GOP party leaders, but also convinced many that the first-time political candidate would soon lose steam. But if his campaign was initially underestimated by the party and political media, it soon became clear that Trump's anti-establishment, populist rhetoric had struck a nerve across the country.
But even as Trump and his campaign celebrate, they now have a more daunting task ahead: defeating Clinton in the general election.
Trump is up against historically high unfavorability ratings and faces immense challenges as he looks to broaden his appeal and base heading into November. The primaries revealed his weaknesses with constituencies like women and minorities.
And since essentially locking up the GOP nomination after the Indiana primary, Trump has confronted various setbacks. He must still to win over key GOP leaders, including House Speaker Paul Ryan, and while he's begun to build out a national finance team, many major party donors and financiers still remain opposed to his bid.