Have the accuser face the accused in court and prove to a jury of 12 people beyond a reasonable doubt that a crime has occured. After which, if the jury finds the accused guilty, a judge will determine what the sentence should be based upon guidlines provided by the law (which is written by congress).

We used to have a system like this. I thought it worked pretty well. Sure it wasn't perfect, but I liked the transparency.

That’s never been the standard for people fighting against America during a war.

For US citizens who are accused of doing that? It absolutely has been, historically. This is especially important in those cases where the accusation is not well-founded, or where the jury would find that the circumstance warrants a lesser penalty than death.

Not in combat. We can debate what “in combat” means, but that is a different issue. If an American picks up a gun, in a war zone, and starts attacking American forces, they can be killed. Full Stop

Oh yes, I agree in the case of your hypothetical scenario - and lethal force would be allowed as well to law enforcement in any domestic gunfight where they start shooting the cops. But the citizen in the article we're all discussing is a journalist, not a gunman. The other famous example of a US citizen targeted for a lethal military strike, Anwar Al-Awlaki, was also in a role that did not personally involve direct engagement in physical violence.

Nothing I'm saying is defending the actions of the citizens in question, only criticizing the propriety of the executive branch unilaterally killing a US citizen without due process outside of situations like your hypothetical where dangerous direct physical violence against American forces is involved. If the government had instead forcibly arrested them and kept them in custody while putting them through the criminal justice system, I'd have no criticism, assuming they had adequate evidence. I'd also want them to release the accused in the unlikely event of an acquittal (since government accusations can be wrong), but the regular courts are very good at convicting people who actually do stuff like this and federal prosecutors are very good at their role.

Right, and we quickly get into the grey area. If the US military has strong evidence that someone overseas is planning terrorist attacks on the US, or US forces, can they attack him first, or is a trial required? This quickly gets very nuanced, but it certainly isn’t black and white.

It certainly can get into grey areas. None of those grey areas pertain to roles like the US citizen journalist which this article is about.

One helpful analogy is to imagine what would happen if we entirely removed the foreign flavor, since after all we're discussing the attempted killing of a US citizen by the US government. Suppose instead that the US military had strong evidence that entirely domestic groups, unlinked to any global extremist Islamist movements, were doing communications or logistics in support of a planned attack a domestic US military base. Maybe this hypothetical attack is due to dissatisfaction with, or skepticism of the legitimacy of, the government in power.

My guess as to what would happen in that scenario: law enforcement would be directed to arrest the people involved and hold them without bail for criminal trial, and would be authorized to use whatever force is necessary if there is physical resistance, including lethal force if necessary. The goal would just be to arrest, however, with killing simply accepted as a possible accidental result.

Something similar would likely have been appropriate here, albeit with the involvement of the military due to the location outside the US and the high likelihood of violent resistance.

If engaged in a situation where your citizens are acting lawfully if someone is shooting at you or about to shoot at you while you are engaged in your lawful action you can shoot them. This is only complicated if you want a reason to go after people for vague reasons.