Approval to target terrorists, U.S. citizens
The president has the constitutional authority to target American citizens overseas.
This authority is derived from his war-making power as commander-in-chief of the armed forces. But this does not mean that the president has unfettered discretion to strike anyone he chooses.
The executive's war-making power is checked by the Founding Fathers' reservation in Congress of the power to declare war. The executive may not use this power unless authorized to do so by Congress.