Many critics of the drone program, myself included, regard these alleged, proposed changes as improvements on the status quo, but let's be clear about exactly how little that actually means. Internal executive branch procedural changes may be prudent, but that does not make them a "check" on President Obama, who can reverse them at his pleasure, as can any of his successors in the White House. If Brennan were truly an advocate of "checking the president's power to kill by drone," he would be calling for constraints to be imposed by the judiciary or the legislature.
Tim Weiner sees the Brennan nomination differently:
Brennan has a once-in-a-generation opportunity to make the CIA what its creators intended: a small, smart, sharply focused espionage organization providing the president with the best intelligence billions of dollars can buy. Let’s hope he succeeds. Because if intelligence fails us again, and we are hit with a third Pearl Harbor, get ready to kiss your cherished Constitutional liberties goodbye.