Our troops on the DMZ and in Pusan are a lot closer, and therefor easier to hit..a "tripwire" is worthess if the otherside isn't playing with a full deck..hell..let's assume the DNK regime implodes...the people revolt..yet in a "gotterdammerung" scenario, crazy Kim decides to go out in a big bang..
Its a tough call.
If I were Pres. they'd remain. Just like if Iran has nukes, I'm glad we are there too, right on there doorstep.
I dont like knowing that our troops could get hurt but I dont like the concept of trying to save our troops from getting hurt when nuking our homes is the other option.