Story highlights Donald Trump has picked up more than 20 unbound delegates since last Tuesday

He currently has 1,080 delegates and on track to clinch the GOP presidential nomination on June 7

(CNN) As Republican leaders grapple with whether or not to support Donald Trump as their presidential candidate, unbound delegates across the country are rallying behind his candidacy, pushing him closer to formally clinching the party's nomination.

Trump has picked up endorsements from more than 20 unbound delegates since he became the presumptive nominee last week, according to CNN's latest count. The real estate mogul gained support from unbound delegates in North Dakota, Louisiana, Pennsylvania and American Samoa. Trump currently has 1,080 total delegates and is on track to clinch the nomination after the last round of primaries June 7.

Most delegates to the Republican National Convention are required to support a particular candidate, based on primary or caucus results from their home state. But about 150 delegates are "unbound," which means they are free to support anyone, and can switch their support at any time.

Trump's largest gain was in American Samoa, the U.S. territory in the middle of the Pacific Ocean. The territory has nine delegates, all unbound, and the delegation decided to unanimously support Trump.

"We are particularly proud to back him, and American Samoa's support shows just how the party from all parts of our country is firmly uniting behind Mr. Trump," said Utu Abe Malae, chairman of the Republican Party of American Samoa.

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