The top military officer in a state is, with one or two exceptions, a two-star general (Major General, or MG) redundantly known as the TAG (The Adjutant General). Idaho's Tag has lately been MG Larry LaFrenz.
MG LaFrenz just announced his retirement, so it is now up to Gov Otter to appoint his replacement. The TAG is a state political appointment, although politics typically plays a smaller role is such appointments than in other political positions. It is not a matter of the next guy in line just moves up.
It is common that a one-star (Brigadier) general (BG)moves up, but not required. A Gov can elevate a colonel to the MG rank, completely skipping the BG rank. Montana's current TAG went that route. He was a lieutenant colonel with the 116th Brigade in Iraq in 2005, came home and made full colonel, and a couple of years later jumped up to the MG rank.
Idaho has 4 BGs; two in the Idaho Army National Guard (IDARNG) and two in the Idao Air National Guard (IDANG). (In Washington, the acronym is WANG. Ha!) There are any number of colonels. Of the 4 BGs that might be considered, the most senior is an IDANG BG who is the commander of the Idaho IDANG. Rumor has it that he is not so much interested in the TAG position.
Without getting into all the details, there are various pay, retirement and entitlement considerations. The TAG is a state employee; 3 of the 4 BGs are full time military, i.e., federal employees.
Anyway, the top IDANG BG probably is not in the running. Next in seniority is IDARNG BG Alan Gayhart, the soldier who commanded the 116th Brigade during its employment to Iraq and currently is the Commander of the IDARNG.
The other two BGs aren't being discussed much as potential replacements. An airman who is being discussed is a colonel who currently runs the Idaho Bureau of Homeland Security, which is an arm of the Military Division and works for the TAG.
The early favorites seem to be the colonel, and BG Gayhart. Some considerations. The last two TAGs were Army, so maybe it's the Air Force's turn. But, there are about twice as many IDARNG as IDANG in Idaho. The IDANG is concentrated around Boise, where the planes and airfield is. The IDARNG is distributed state wide; all larger cities, IF, Poky, Twin Falls, Lewiston (not sure about CdA), and lots of smaller towns; Post Falls, Payette, Hailey, Burley, Blackfoot, and many more.
I don't know much about the IDANG colonel, other than he is currently running a good-sized state agency and used to be the Joint Forces (both IDANG and IDARNG share a single headquarters commanded by the TAG) chief of staff. Rumor has it that he's politically active and has developed some connection with Gov Otter. Not that he's a hack or an operative, he's just politically connected. From what I know of him, he's been a fine Air Force officer.
I do know BG Gayhart.* As mentioned, he commanded the Brigade in Iraq. Given that the Brigade is going back to Iraq next year, it might be important to have the TAG have combat leadership experience. BG Gayhart very successfully commanded that deployment. I could go on for many paragraphs about BG Gayhart's many and diverse qualifications, but suffice it to say, he would be a very good choice.
* Disclaimer. He is currently in my chain of command. But, I'm almost at the end of my military career, I cannot be promoted again, and I've obtained the highest position I will, so I don't really have anything to gain from brown-nosing BG Gayhart. I just think he'd be an outstanding choice, and I think he deserves the promotion.