Admiral Sandy Winnefeld, USN (ret.), former Vice Chairman of the Joint Chiefs of Staff and now distinguished professor in the Sam Nunn School of International Affairs, wrote "President Trump draws his red line" for The Hill.
Find an excerpt:
Whether one agrees with the elimination of General Qassem Soleimani as the correct means of signaling Iran, it was an important statement that a new red line is in effect. Proxy warfare – namely, a client organization taking hostile action in a manner hard to directly attribute to, but that everyone knows was ordered by, the patron – has always been convenient for these states.