FYI, Department of Defense Directive 1344.10, dated February 19, 2008, covers the permissible political activities for uniformed service members.
It is DoD policy to encourage members of the Armed Forces (hereafter referred to as “membersâ€) (including members on active duty, members of the Reserve Components not on active duty, members of the National Guard even when in a non-Federal status, and retired members) to carry out the obligations of citizenship. In keeping with the traditional concept that members on active duty should not engage in partisan political activity, and that members not on active duty should avoid inferences that their political activities imply or appear to imply official sponsorship, approval, or endorsement, the following policy shall apply:
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4.1.2. A member of the Armed Forces on active duty shall not:
4.1.2.1. Participate in partisan political fundraising activities (except as permitted in subparagraph 4.1.1.7.), rallies, conventions (including making speeches in the course thereof), management of campaigns, or debates, either on one’s own behalf or on that of another, without respect to uniform or inference or appearance of official sponsorship, approval, or endorsement. Participation includes more than mere attendance as a spectator. (See subparagraph 4.1.1.9.)
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4.1.2.5. Speak before a partisan political gathering, including any gathering that promotes a partisan political party, candidate, or cause.
4.1.2.6. Participate in any radio, television, or other program or group discussion as an advocate for or against a partisan political party, candidate, or cause.
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4.1.2.15. Attend partisan political events as an official representative of the Armed Forces, except as a member of a joint Armed Forces color guard at the opening ceremonies of the national conventions of the Republican, Democratic, or other political parties recognized by the Federal Elections Committee or as otherwise authorized by the Secretary concerned.
Attending a rally
in uniform, giving a partisan speech in favor of a candidate
in uniform, endorsing a candidate while
in uniform, all of this violates the guidance.
Thanks to Odysseus (an Army LTC) over at Conservative Underground.