threats to the President have been publicized, including the well known alleged plot by white supremacists in Tennessee to rob a gun store, shoot 88 black people, decapitate another 14 and then assassinate the first black president in American history.
Most however, are kept under wraps because the Secret Service fears that revealing details of them would only increase the number of copycat attempts. 
According to the U.S. Secret Service agents, their goal is to immediately respond to any direct threat against the president, the first family, the vice president, or visiting heads of state. Agents are then responsible for determining the credibility of the threat. 
Each time there is a threat, the Secret Service consults with the Protective Intelligence Division in Washington, D.C., to decide how far an investigation is going to go. If a federal arrest takes place, it will lead to the most serious or extreme of the end results.
Recently, when Anton Caluori, 31, allegedly emailed the FBI on the morning of August 21st to say he would "kill the president," a Secret Service agent was immediately dispatched to his residence. According to the Department of Justice, Caluori was armed with multiple weapons, making his threat not only credible, but viable. 
"This case had all the troubling ingredients: threats of violence and explosive devices, multiple weapons with hundreds of rounds and even brandishing of a weapon at law enforcement," said U. S. Attorney Jenny A. Durkan.
Caluori was subsequently arrested and charged in federal court with making a threat against the president and assault of a federal agent. If convicted, he could face up to 25 years in prison. He is scheduled to appear in federal court in Seattle Monday for a detention hearing. 
Recent national events are a stark reminder that the Secret Service has to take these threats of death or violence seriously. While the Secret Service says they take every threat against the president seriously, not all will end in arrest. Threats will come our way from high school students, even junior high school students in the way of prank type calls. There are threats on Twitter and on Facebook and other social sites that allow such comments, but they have to look at them all. People need to know that any type of threat against the president is a violation of federal law. 
The Secret Service says that many of those who make such threats are mentally ill, and it is the goal of the Secret Service to find them help. It can be "sobering," they said, when agents show up at their door. 
According to the Secret Service, the president is the most threatened person in the U.S., regardless of political party. 
The President is not made aware of all threats against him, however, because as the Secret Service says, "the sheer number would be overwhelming and, frankly, distracting."