Suddenly, the dark fills with spies who are paid to hear things and report them down at Security. Don Enrique claims Trujillo needs help in running this country. Don Enrique's daughter says it's about time women took over the government. Words repeated, distorted, words recreated by those who might bear them a grudge, words stitched to words until they are the winding sheet the family will be buried in when their bodies are found dumped in a ditch […]. (1.1.66)
The family must watch its mouth even when they are alone in their own front yard. Trujillo's fearful power is demonstrated in the paranoia that people feel after anyone criticizes the regime; even if they are alone they immediately fear that he might have spies posted.
"Tell me, Sinita, maybe it'll help."
"I can't," she whispered. "We can all be killed. It's the secret of Trujillo." (1.2.49-50)
Trujillo's secret is that he came to power through killing anyone who stood in his way, and it is such a terrible secret that it gives him power. Once anyone knows the secret they are terrified to talk about it or to defy him… which just makes him that much more in control.
"My uncles, they had a plan to do something to Trujillo, but somebody told on them, and all three were shot, right on the spot." (1.2.56)
Here we can see Trujillo's handy spies in action. When Sinita's uncles had a plan to stop Trujillo's march to absolute power, "somebody" told on them—it doesn't matter who, just that Trujillo has eyes and ears everywhere. And his revenge is swift and terrible, too.
According to Sinita, Trujillo became president in a sneaky way. First, he was in the army, and all the people who were above him kept disappearing until he was the one right below the head of the whole armed forces. (1.2.59)
Did you ever play Risk? Yeah, you're never going to finish that game you started last summer, but take a break for a quick chat about strategy. The players who win know how to corner everyone, picking them off one by one and consolidating their power. That's exactly what Trujillo was doing.
At first the sisters were frightened. But then, they started receiving gifts, too: bolts of muslin for making convent sheets and terrycloth for their towels and a donation of a thousand pesos for a new statue of the Merciful Mother to be carved by a Spanish artist living in the capital. (1.2.95)
The sisters (not to be confused with the Butterflies; we're talking nuns here) are protective of their students at first, but they are easily swayed by Trujillo's display of power. See, power isn't always just assassinations and bullying; it can also be used to bribe people to look the other way.
In his big gold armchair, he looked much smaller than I had imagined him, looming as he always was from some wall or other. He was wearing a fancy white uniform with gold fringe epaulets and a breast of medals like an actor playing a part. (1.2.132)
When Minerva finally sees Trujillo in person after only having seen photographs of him (although there were lots of photographs of the guy hanging around the country), she is surprised by how small he is compared to his personality. The uniform is a costume and the president is playing a part. Is power just an act in the end?
I see the picture of our president with eyes that follow me around the room, and I am thinking he is trying to catch me doing something wrong. Before, I always thought our president was like God, watching over everything I did. (1.3.107)
When Mate finds out that the president isn't such a great guy (what with all the murdering he's been doing) she finds it hard to believe. For her, he was so powerful that she thought of him as godlike, all-powerful. And when the all-powerful turn out to be evil, it's a pretty frightening prospect.
Then there had been the silence that always followed any compromising mention of the regime in public. One could never be sure who in a group might report what to the police. Every large household was said to have a servant on double payroll. (2.5.94)
"Double payroll" comes up regularly in the novel. It's the idea that a person can be working in one job, collecting a paycheck there, but reporting everything they see on the job to Security and getting another paycheck there. Trujillo maintained his power by employing spies everywhere.
Mamá wanted to get me a medical excuse from Doctor Lavandier. After all, migraines and asthma attacks weren't against the law, were they? "Trujillo is the law," Papá whispered, as we all did nowadays when we pronounced the dreaded name. (2.6.54-55)
One of the most despicable abuses of power that Trujillo committed was the way he forced young girls into having sex with him by instilling them with fear of their families being punished if they refused. When he explicitly invites Minerva to a party, Mamá knows exactly what it means and wants to protect her daughter from the bad dude. The dad is more practical though, seeing Trujillo's desire as synonymous with the law—there's no escape.
He rises from his chair, and I am so sure he is going to ask me that I feel a twinge of disappointment when he turns instead to the wife of the Spanish ambassador. Lío's words of warning wash over me. This regime is seductive. How else would a whole nation fall prey to this little man? (2.6.102)
At the party, Minerva sees Trujillo's power at work. She hates the guy, and is actually working against him in secret, but when he chooses to dance with someone else she feels rejected. That game of making people feel chosen and rejected is one way that Trujillo seduced the nation, gaining ultimate power.