TAIPEI, Taiwan — A doctor and political novice is favored to win Taipei’s mayoral election on Saturday, one of many races in which Taiwan’s governing party faces the prospect of its most serious setback in years.

A victory for the blunt-talking, 55-year-old physician, Ko Wen-je, would be a sharp defeat for the governing party in a city long considered its stronghold, and in a job that often becomes a springboard to the presidency.

The local elections come halfway through President Ma Ying-jeou’s final term as president, during a year in which his governing Kuomintang, or Chinese Nationalist Party, has faced large-scale protests over its pursuit of closer ties with China, and food-safety scandals that have inflamed antigovernment anger.

In the race for Taipei mayor, the governing party’s candidate is Sean Lien, a 44-year-old former investment banker whose father, Lien Chan, served as Taiwan’s premier and vice president. While his connections helped him win the party’s nomination, they have done little to bolster his standing against Mr. Ko.