What is the left shoulder sleeve insignia worn by this very fine looking officer?

Reagan is wearing the 8th army patch while the troops around him are wearing 2nd INF DIV patch . The photo was taken somewhere close to the Korean DMZ .

The patch is the 8th Army. What you don't see is the front of the jacket, where on the right front is the Second Infantry Division (2ID) patch.
The photo was taken at Camp Liberty Bell. The unit assigned to the DMZ mission at the time was 1st Bn 38th Infantry, Rock of the Marne, 2nd BDE, 2nd ID.
I was assigned to the 2nd Brigade, 2ID to be a driver for the BDE Commander at the time, and was lucky to have been there and seen President Reagan.
He was a great man and one of the greatest President we have ever had. I wish someone like him was running for President today.

The patch is the 8th U.S. Army Korea patch I wore that patch at one time it also affectionately called the Cookie Cutter patch.

8th Army

I was proud to serve in the Air force and have this great man as my Commander in Chief.

I believe that it is 8th army in Korea.

Eighth US Army (EUSA) in Republic of Korea.

8th army

8th U.S. Army

that patch is easy to look up and anyone that's been to Korea knows thats 8th Army