Still, the federal government has not scheduled an execution under Obama, who says he supports capital punishment in rare cases. Since at least 2010 the Justice Department has been reviewing its execution protocols, thanks to a nationwide shortage of the lethal injection drug sodium thiopental. The death penalty has also grown politically controversial, as the advent of reliable DNA evidence testing has exposed wrongful convictions in capital cases. Polling still shows nearly two-thirds of Americans support executions in murder cases, but that number is down from a 1992 peak of 80 percent. (A majority of Americans have not opposed capital punishment since the mid 1960s, according to Gallup.)

While putting a convicted terrorist to death might seem highly uncontroversial, there is one practical argument against it: that foreign anti-death penalty governments might refuse to extradite terror suspects to America. Secretary of State John Kerry held this position as a U.S. Senator until he ran for president in 2004. Indeed, during the trial of the “20th hijacker” Zacarias Moussaoui, Germany and France supplied prosecutors with evidence only on the condition that it not be used to support his execution. (Moussaoui was sentenced to life in prison.)

Defense lawyers tell the Boston Globe that Dzhokhar Tsarnaev’s legal team might try to spare his life by emphasizing his age (nineteen) and the apparent leadership of his deceased older brother. They may also urge him to plead guilty: several notorious killers, including the Unabomber Ted Kaczynski, the Atlanta Olympics bomber Eric Rudolph, and the Tucson shooter, Jared Loughner, all pleaded guilty to their crimes and avoided likely death sentences as a result. In a 2011 Justice Department memo Holder wrote that “a defendant’s willingness to plead guilty will now expressly be recognized as a factor” in deciding whether to pursue capital punishment.