5th amendment provides for due process for americans so it is a defendable interpretation of the constitution. I agree it's tricky because the guy was openly al Qaeda. Paul's stated objection was the precedent set that American citizens can be assassinated when a president deems them a threat, and how over time incrementalism could end up with frightening implications at home, like for example deeming members of the media threats. Can't totally dismiss that, look what incrementalism has done to our budget.