GUATEMALA CITY — Just about every weekend for months, Jorge Castiglione, a 70-year-old engineer with a thinning ponytail, has gone to the Plaza de la Constitución here to support what has become a ritual in this nation: weekly protests calling for the resignation of the president and an end to political impunity.

These might seem rather ambitious demands. Politics here are as corrupt as dissent is deadly, at least if the last half-century is any indication. When protests began a few months ago, set off by revelations about a vast customs fraud scheme, few, including Mr. Castiglione, figured things would change.

But suddenly, they did. And fast.

Spearheaded by a United Nations-backed commission, investigations into corruption expanded to the highest levels of government. On Friday, the nation’s former vice president was arrested, and prosecutors claimed that the president, Otto Pérez Molina, was the chief beneficiary of a fraud ring that siphoned millions of dollars in customs revenues while basic public services suffered.

For a nation with the cards stacked against it — among the highest poverty and murder rates in the hemisphere and a history of violent government repression — the emergence of large public protests is being greeted as a major step. But a pressing question looms: Will the momentum continue? After the high-profile arrests and the emergence of peaceful protests in a place silenced by a history of civil war, will lasting change occur?