Maybe it has to happen every year or two. At least in wartime. Some sailor, soldier or Marine decides to challenge the president of the United States, publicly, on some issue or other, and has to be disciplined. From time to time it may even be a general. (See MacArthur, Douglas.)

Last time this came up -- was it 2010? -- it was a lieutenant colonel, and a doctor to boot, who declined to deploy to Afghanistan. The now decidedly former Lt. Col. Terrence Lakin theorized in his wisdom -- clearly his degree was in medicine, not political science or military law -- that the commander-in-chief's birth certificate wasn't valid, so neither was his presidency. So he wouldn't follow a direct order.

OK. The colonel was deployed to prison instead. Fair enough, legal enough, necessary enough.

Generals and colonels have to follow orders, too, just as they expect their orders to be followed by majors and sergeants. The country can't have its military deciding, from trooper to trooper, whether to follow orders and deploy when those orders are cut. No matter what a grunt might think about war, any war, a member of the armed services is expected, should be expected, to have one response when called on by the president of the United States to take his post: Yes, sir.

When our all-volunteer force puts on the uniform, each trooper knows the drill, and the deal: You lose some rights. You don't have the First Amendment right to speak your mind when standing at attention in formation. You don't have the right to avoid Unreasonable Searches and Seizures when your drill sergeant starts emptying your sock drawer and throwing the contents across the room. And if the MREs they give you in the field don't violate the Eighth Amendment's guarantee against cruel and unusual punishment, what does? There's no appeal in this man's army. A soldier is a soldier. A Marine is a Marine. Twenty-four-seven. Just as a doctor is always a doctor. Or a judge a judge, on the bench or off. Some of us are always on duty. And are expected to act like it.

The latest to learn this lesson that every recruit should've learned (before he even signed up) is one Gary Stein, a 26-year-old Marine. A military board of review has recommended that he be dismissed from the service with an Other Than Honorable discharge.

What'd he do? Or rather not do. For starters, he seems to be still another birther. And a public one at that. Because he posted stuff on the Internet questioning President Obama's birth certificate. He then went to Facebook -- ah, the ubiquitous, always treacherous, all-revealing Facebook! -- and posted a claim that the president is a liar. For bad measure, he added that his commander-in-chief is just the kind of Domestic Enemy that the military's oath mentions when those who take it swear to protect the Constitution of the United States.

Oh, dear.

It's one thing to think such things. The mind is, and always should be, free. It's another foolish, insubordinate thing to say it. It crosses a clear line when you say it publicly -- on the Internet, yet.

That's grounds for dismissal. And should be.

This being America, the sergeant has lawyered up. And one of his attorneys told the press: "I don't think any law was violated by Gary Stein. The reason we have this reticence in the military to get engaged in politics is that we were afraid a long time ago of military dictatorship. We are so far from that in suggesting that on a private Facebook page, you can't say something about politics."

Lordy, lordy, where to start? How about here: A private Facebook page?

If that Facebook page was private, or shielded, or whatever the term, how did the authorities find out about it? Did somebody copy the message? Or like it or friend it or share it? There are a million ways to share incriminating or just embarrassing stuff once somebody posts it online. Welcome to the age of the Internet, counselor. Surely you've heard of it.

This case is just why we have the sort of thing that's generally called Conduct Unbecoming. You don't have to break a specific law to be given your walking papers by the U.S. military. There's no spelling out every type of insubordination in a code of law. But surely you can tell it when you see it, especially on Facebook. The consequence is dismissal. To use a phrase a lawyer might recognize, it's called dismissal at will.

Unfortunately, Sgt. Stein's lawyers weren't the only ones heard from. There was Sgt. Stein himself:

"The allegations drummed up against me are no more than an agenda by the Marine Corps to use me as an example. If I am guilty of anything it would be that I am American, a freedom-loving conservative, hell-bent on defending the Constitution and preserving America's greatness."

Nice speech. Run for office. But not in uniform.

Marine (for now), you may be an example, all right, but not a good one. The brass would be well-advised to use your case as a Teachable Moment in its orientation sessions. Yes, the Marine Corps may very well have an agenda when it comes to discouraging those in its ranks from insulting its commander-in-chief, or anybody else in the chain of command. It better.

This is called military discipline. And the United States Marine Corps has a reputation for being the best disciplined of all the branches. First in, last out, Halls of Montezuma, Shores of Tripoli, and above all Semper Fi. Which is why one Gary Stein soon may no longer be a Marine.

Want to insult the commander-in-chief and president of the United States? Fine. It's every American's right and, from time to time, maybe even habit.

Just do it in civvies.

Dismissed.