Selection of the unpledged add-on delegate occurred at the Assembly of the Democratic Party of the Commonwealth of Puerto Rico on June 21, 2008, in San Juan.

[4] In a poll conducted from March 31–April 5, 2008, Clinton led Obama by 13%, holding 50% to his 37%, with 13% undecided and a margin of error of ± 4.4%.

[5] In a poll conducted from May 8–May 20, 2008, Clinton led Obama by 13%, holding 51% to his 38%, with 11% undecided and a margin of error of ± 3.4%.

Four superdelegates, Democratic State Chair Roberto Prats, Vice Chair Luisette Cabañas, Puerto Rico Democratic National Committeeman Kenneth McClintock and Young Democrats of America (YDA) National Committeeman Francisco Domenech, a majority, had announced support for Sen. Hillary Clinton and the remaining 2, Governor Aníbal Acevedo Vilá and National Committeewoman Celita Roque, had announced support for Sen. Barack Obama.

In the Clinton campaign, the candidate's daughter, Chelsea, and her spouse President Bill Clinton, both travelled twice to Puerto Rico and during one extensive campaign day, May 26, the three attended several events together in Ponce and San Juan, according to a book by Democratic State Chair Roberto Prats and Senate President Kenneth McClintock.