A popular revolt against the imposition of same-sex marriage has transformed the political landscape of Costa Rica , propelling a once-obscure Christian evangelical singer to a first-place finish in presidential voting this month and putting the outspoken critic of gay marriage in a strong position to win the spring runoff. In a crowded field, Fabricio Alvarado catapulted from afterthought to front-runner in the wake of a January ruling that seemed to pave the way for same-sex unions in the largely Catholic Central American nation.