(CNN)Growing concern that top U.S. military leaders are increasingly being asked to comment on proposals by presidential candidates has led the chairman of the Joint Chiefs of Staff to draft a letter to all troops with one message: Stay out of politics. Gen. Joseph Dunford is expected to issue a note to all military forces as soon as this week. Dunford will "remind the troops of the need to remain apolitical in order to sustain Americans' trust and confidence in them," said the chairman's spokesman, Capt. Gregory Hicks. The U.S. military has a longstanding tradition of remaining out of politics...