When Magsaysay died due to a plane crash in 1957, Vice President
Carlos P. Garcia soon assumed office as President. With the
presidential election scheduled to be held in the same year, Magsaysay's death also triggered a chaotic political situation in the country, most notably with the ruling
Nacionalista Party. Manahan, among other Nacionalistas closely associated with Magsaysay, were disappointed by the "cold treatment" given to them by allies of President Garcia and decided to leave the party. Soon, Manahan co-founded the Progressive Party of the Philippines together with Raul Manglapus. The new party aimed to be an alternative to the Nacionalista Party and the
Liberal Party. Manahan served as its candidate for the presidential election, with Vicente Araneta as his running mate. Despite having less money compared to the candidates of the two major parties, he was able to rally significant support among the masses with his popular appeal and his resemblance, both physically and ideologically, to the late President Magsaysay. On September 7, 1957, Manahan survived an assassination attempt while campaigning in
Opon,
Cebu. Andronico Baguio, the would-be assassin, attempted to kill Manahan with a 7-inch knife. However, he was quickly apprehended by Manahan's bodyguards. Manahan eventually asked the police to release Baguio as soon as they confiscated his knife. Manahan lost to Garcia in the presidential election, managing to rank in 3rd place with 20.90 percent of the vote. Araneta, his running mate, lost to
Diosdado Macapagal of the Liberal Party. == Senatorial career ==