In this interview with Al Carroll, author of President's Body Counts: The Twelve Worst and Four Best American Presidents Based on How Many Lived or Died Because of Their Actions, US presidents are reviewed on a wholly new basis.

Peter Handel: What caused you to take what could be termed a rather unusual approach to presidential history?

Al Carroll: Presidents are routinely ranked every year, and it's often partisan. The Federalist Society even named [George W.] Bush the sixth greatest president of all time, during the worst of the Iraq War. Too many of these rankings are simple-minded, "Let's cheer for our side or point of view."

We need both an objective way to rank and an imminently practical one. Who lived better as a result of these men's actions? Better yet, who lived or died because of them?

A key perspective you write from is how the concept of genocide is defined. Could you briefly elaborate on how you frame the definition and its subsequent manifestations?

Genocide was a term coined by Raphael Lemkin right after the Holocaust. What was important to me is that the reader see how governments and leaders try to avoid using it because admitting genocide is going on in places like Darfur requires them to take action to stop it. Many Americans are also reluctant or were never taught that genocide has happened here, in America, and was worst of all in California. There were also some presidents that ignored genocides, as recently as Clinton ignoring Rwandan genocide.

Which president's actions do you consider the most egregious?

Nixon was the worst by far for what he did in Cambodia, what many argue was outright genocide. He ordered the carpet bombing and invasion of a neutral nation for no other reason than to convince conservatives he was still tough on communism. Half a million were killed, including 50,000 executions.

Nixon also ignored genocide against Bangladesh, continued a program of mass torture far worse than GW Bush's, ordered chemical warfare in Vietnam, and pardoned a mass murderer of women and children, Lieutenant Calley at My Lai.

Reagan was a close second for collaborating with genocide in Guatemala. But he did not initiate it as Nixon did in Cambodia.