The Justice Department "white paper" purporting to authorize Obama's power to extrajudicially execute US citizens was leaked three weeks ago. Since then, the administration – including the president himself and his nominee to lead the CIA, John Brennan – has been repeatedly asked whether this authority extends to US soil, i.e., whether the president has the right to execute US citizens on US soil without charges. In each instance, they have refused to answer.
Brennan has been asked the question several times as part of his confirmation process. Each time, he simply pretends that the question has not been asked, opting instead to address a completely different issue. Here's the latest example from the written exchange he had with Senators after his testimony before the Senate Intelligence Committee; after referencing the DOJ "white paper", the Committee raised the question with Brennan in the most straightforward way possible: