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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.

In North Dakota, a handful of delegates that originally supported Cruz told CNN they are now planning to vote for Trump at the Republican convention in Cleveland. Trump also picked up endorsements from two other North Dakota delegates that had previously been uncommitted.

Cruz claimed a “resounding victory” in North Dakota, and he performed well at their state convention in April. But because their delegates are unbound, they can switch support as the race changes.

“Even as an initial Cruz supporter, I recognize the gravity of our situation in the Supreme Court and will do whatever it takes to ensure that Hillary Clinton does not become president,” said John Trandem, an unbound delegate from North Dakota who says he will back Trump once he clinches the nomination.

Trump picked up support from five unbound Louisiana delegates that were originally pledged to Sen. Marco Rubio. He also got endorsements from two unbound delegates that were elected in Pennsylvania’s convoluted primary on last month.

This was a group closely watched as Cruz and John Kasich sought to keep Trump from reaching the 1,237 delegates needed to win the nomination on the first ballot. Cruz especially had a strong ground game that was winning commitments for the Texas senator.

Still, not everyone is on board with Trump as the Republican nominee, with some saying the onus is on Trump to win over party loyalists.

“He needs to demonstrate that he truly is going to support our other Republican candidates, and that he realizes how important it is to keep control of the Senate,” said Mary Ann Meloy, an unbound delegate from Pennsylvania who is still uncommitted. “He hasn’t demonstrated very much respect for other elected leaders.”