In 1958, Tomás was chosen by then-Prime Minister António Salazar as the candidate of the ruling National Union party for the presidency of the republic, succeeding Francisco Craveiro Lopes. He ran against the opposition-backed Humberto Delgado. It initially appeared that the election ended as soon as Tomás was nominated since the electoral system was so heavily rigged in favor of the National Union that he could not possibly be defeated. However, in an unusually spirited contest, Tomás was ultimately credited with 76.4 percent of the vote to Delgado's 23.5 percent. Most neutral observers believed, however, that Delgado would have won had the election been honest. Salazar was alarmed enough that he pushed through a constitutional amendment transferring the election of the president to the legislature, which was firmly controlled by the regime. Tomás was re-elected by the legislature in 1965 as the only candidate.