Nobody’s saying that US citizens who defect to the enemy maintain some kind of shield of immunity in a battlefield context. Nor is anyone denying that the US government has the authority to arrest people it believes to have committed crimes. So why not send a bunch of troops into the relevant part of Yemen seeking to either create a context of stability in which al-Awlaki can be arrested or else perhaps he’d be killed on the battlefield? Well, because nobody seems to think that would be smart policy. Which is presumably because al-Awlaki isn’t in fact all that dangerous so policymakers don’t think it makes sense to engage in costly measures to kill or capture him.
Alex Massie has a view from across the pond:
Awlaki does not seem an especially attractive customer but if the American government has the power to determine any location on earth a battlefield environment so that it can assassinate its countrymen without fear of judicial repercussions then evidently there are few remaining limits on Presidential power and whatever small - and foolish - hopes you might have for the end of the Imperial Presidency should be locked away for years yet.