One of the great things about the United States at the time of its foundation was that unlike the absolute monarchies it was replacing, the king President couldn't just have someone locked up or killed solely on their own say-so. There were no lettres de cachet in America. If the government wanted to punish you, they had to do it by law, through the courts, with proper checks and safeguards.
The director of national intelligence affirmed rather bluntly today that the U.S. intelligence community has authority to target American citizens for assassination if they present a direct terrorist threat to the United States.(Emphasis added)"We take direct actions against terrorists in the intelligence community; if … we think that direct action will involve killing an American, we get specific permission to do that," Director of National Intelligence Dennis Blair told the House Intelligence Committee.
So, the US President is signing death warrants of American citizens, without any independent test of the evidence or judicial oversight. In other words, he's authorising extrajudicial executions. This isn't just one of the hallmarks of tyranny, it's also a fundamental violation of US law and the US constitution. And those responsible need to be held to account for it on charges of murder.
(Glenn Greenwald has more here).