A conviction, which many legal observers and Mr. Zamora himself say is the likely outcome, would be another blow to Guatemala’s already fragile democracy, according to civil rights advocates, as the government and its allies have taken repeated aim at key institutions and independent news media outlets.

The trial also comes as the country heads toward a presidential election this month that has already been plagued by irregularities, with four opposition candidates disqualified ahead of the race.

“The rule of law is broken,” said Ana María Méndez, the Central America director at WOLA, a Washington-based research institute. Mr. Zamora’s case represents, she added, yet another “step toward the consolidation of a dictatorship” in Guatemala.

Unlike other Central American countries, like Nicaragua and El Salvador, where democracy has also eroded, however, power is not concentrated in a family or an individual, Ms. Méndez said.

In Guatemala, she added, “authoritarianism is exercised by illicit networks made up of the economic elite, the military elite and organized crime in collusion with the political class.”