[2] The SET decision was based on the evidence presented by Pimentel in his protest showing many ballots were spurious.

GO's Antonio Trillanes and Koko Pimentel, and Migz Zubiri of TEAM Unity were contesting the last two Senate seats.

In the final tally for the 2007 senatorial race by the Commission on Elections (COMELEC), Zubiri narrowly edged out opposition candidate Koko Pimentel for the 12th and last slot in the Senate.

After oral arguments however the High Tribunal again voted to uphold the COMELEC's decision to proclaim Zubiri, consequently failing to grant Pimentel's petition.

[6] However, the Court's judgment did not prevent Pimentel from bringing his poll protests to the Senate Electoral Tribunal.

[8] On March 14, 2008, the Supreme Court in a 40-page decision penned by Associate Justice Minita Chico-Nazario, dismissed Koko Pimentel's petition to stop the Commission on Elections from canvassing votes from the province of Maguindanao,[9] a definite morale booster for Senator Zubiri.

Zubiri cited the issue dividing the nation and placing doubts on the electoral system as the reason for his resignation.

"[15] Senate President Juan Ponce Enrile immediately announced that he will study on what to do next as there is no precedent; Senator Francis Escudero, on the other hand, said that Zubiri's resignation is effective immediately, citing instances where senators left office to accept other positions such as when Raul Manglapus became Foreign Affairs Secretary, Alfredo Lim became Mayor of Manila, Teofisto Guingona became vice president, and when then-Senator Aquino was inaugurated as president.

Commission on Elections Chairman Sixto Brillantes said that the resignation implies that fraud did occur in 2007 and that will benefit Pimentel.

In 2019, Zubiri endorsed Pimentel under the banner of the administration party, Coalition for Change (Philippines) who won and defended him from the allegations that he is prohibited from running for reelection on that year.