Well Libya was a UN mission that went damn well without stepping foot in the country and costing less than a billion dollars. And for the first time in my lifetime, we let other countries take the damn lead so the burden wasn't so much on us. We did the first two days of air support along with Europeans and from then on all we did was supply raw materials to rebels and provide satellite intelligence that eventually was responsible for telling the British and Libyans where Gaddafi was so they could bomb and intercept him respectively. It was IMO one of the smartest uses of force in a long time and set the president that not every mission has to be US led.

NDAA passed with a very veto proof majority of 80+ Senators and roughly similar proportions in the House. If he did veto it, it would have shut down VA hospitals, veteran's benefits, paychecks to the families of those currently serving and payment to all those supplying the military that would have cost tens of thousands of jobs to end overnight. All that and his veto would still have been overridden, it would have been a pointless stand with huge negative ramifications without changing the end result.

As for the assassination of Anwar al-Awlaki (to date the only assassinated US citizen), that was an attack on someone who was otherwise outside our ability for the legal system to reach (we don't have authority in Yemen) and was an active and public member of Al Qaeda. It's not like there are snipers on the roofs of buildings picking off people the President just happens not to like.

Al Qaeda and other trans national militant groups are hard to know how to handle. As it stands there is not treaty or convention outlining how you go after them. You can't rely on the national governments where they happen to be because often the governments are in a state of failure or near failure in the areas where groups like that congregate. So the rules of war don't quite apply because it's not a nation, and the rules of criminal justice don't quite work either because they will never be within the reach of the legal system.

Reagan, Bush HW and first term Clinton tried to stick to the criminal mindset. Clinton by his second term was beginning to realize that there must be an element of military response because failed states will never cooperate with the legal system, following the 2000 bombing of the USS Cole he said that if the Afghani government does not turn over Bin Laden and other top leaders he would hold the country responsible for the next attack. Bush W rescinded that executive order, but followed it's conclusion none the less and the world was willing to hold the Afghan Government (to the extent that there was a government) responsible by sheltering Al Qaeda and so it was clear we were to invade. But Afghanistan was a unique instance, despite willingness to use military force since the second Clinton term there is still no general guideline on how to go after members of transnational military organizations. The fact that one of the people we went after had American citizenship shouldn't be seen without the context of the discussion we should be having about what approach to use.

In past times of war, when war was nation to nation and clear, if a citizen enlisted in a foreign army at war with the United States they would lose their citizenship. Treason has also always been grounds for the revocation of citizenship, but if someone fails to participate in their trial a traditional civilian court to find someone guilty of treason can't happen. There is nothing the legal system has the power to do to go after someone like Anwar al-Awlaki. That leaves two options, leave him alone indefinably or go after him militarily. Neither is tasteful but when it was as clear cut as Anwar al-Awlaki I think the right call was made.