Trump has now secured the backing of 1,238 delegates, one more than the 1,237 needed, according to the AP, which said the New York real estate tycoon passed the threshold when a small number of unbound Republican delegates, including Oklahoma GOP chairwoman Pam Pollard, said they would support him at the convention.
Trump was already the Republican presumptive nominee, capping a spectacular and unlikely campaign for the White House that has thoroughly upended American politics.
He was assured of reaching the magic number of 1,237 delegates at the latest on June 7, when California and four other states hold Republican primaries.
CNN’s estimate currently puts Trump at 1,229 delegates, eight shy of the threshold.
Trump bested 16 Republican rivals in the race. The last stragglers, Senator Ted Cruz and Ohio Governor John Kasich, dropped out early this month after Trump won Indiana.
But the provocative frontrunner has struggled to win the support of key party establishment figures, including House Speaker Paul Ryan, who have voiced concern about the presumptive nominee’s tone and his lack of policy specifics.
Trump was due to deliver a speech on energy later Thursday in Bismark, North Dakota.
His likely Democratic rival in the general election, former secretary of state Hillary Clinton, is set to lock in the nomination following the June 7 primaries.