Friday afternoon, in a letter to Speaker John Boehner, President Obama announced that he’ll be deploying 100 combat-ready U.S. soldiers, mostly special forces operators, to Uganda, South Sudan, the Central African Republic, and the Congo.

So much for Dinesh D’Souza’s pet theory that “Kenyan anti-colonialism” is the secret motivation behind everything the president does.

The soldiers’ mission is to help Ugandan forces round up the so-called Lord’s Resistance Army, a group that few Americans had heard of before last week.

The LRA, a grotesque death-cult led by Joseph Kony, a self-proclaimed “spokesperson” for God, has, as Obama put it, “murdered, raped and kidnapped tens of thousands of men, women and children in central Africa” over the last 20 years.

Our soldiers aren’t supposed to engage LRA forces, except in self-defense, and, given that LRA lore holds that anointing yourself with shea nut oil will make you bulletproof, U.S. special forces can probably handle any trouble they get into.

But, following on the heels of Libya — a war in a country the president’s own secretary of defense admitted is “not a vital interest for the U.S.” — Obama’s Ugandan adventure raises the question, what in the world does he think the American military is for?

The LRA is surely a horrible bunch, but, equally surely, they’re no threat to American national security. The president’s decision — in the midst of two ongoing wars — to involve U.S. soldiers in another fight where America has no possible stake, suggests a disturbingly incontinent approach to military intervention.

If so, the incontinence is bipartisan. Obama’s letter to Boehner, intended to serve as notification under the War Powers Resolution, invokes the Lord’s Resistance Army Disarmament and Northern Uganda Recovery Act of 2009. That act, which endorsed “military and intelligence support” for efforts to neutralize the LRA and capture the movement’s crazed leader, passed by a wide margin, with 64 co-sponsors in the Senate, 201 in the House.

And the president’s Friday announcement got emphatic support from Sen. James Inhofe, R‑Okla., one of the Senate’s staunchest conservatives.

As the Atlantic’s Max Fisher noted, the deployment reflects “a small but important shift in how, where, and why the U.S. uses military force.”

The Obama team has embraced the U.N. doctrine known as “Responsibility to Protect,” which holds that the “international community” has an obligation to protect civilians from crimes against humanity — by force, if necessary — when their own governments cannot or will not.

That doctrine is at odds with the U.S. Constitution, which empowers Congress to set up a military establishment for the singular end of “the common defence … of the United States.”

Even so, the emerging Obama Doctrine reflects a fondness for feel-good “humanitarian interventions,” through which we prove our nobility by putting blood and treasure at risk when there’s nothing in it for us.

These expeditions tend to go OK — until they don’t. Recall that it was the hunt for Somali warlord Mohamed Farrah Aidid that led to the “Black Hawk Down” incident, with 18 U.S. soldiers killed and 80 wounded in 1993.

A similar disaster seems unlikely here, and our Ugandan incursion may well do some for the LRA’s long-suffering victims. Yet success breeds boldness, and with each new intervention, our defense establishment is becoming further unmoored from its constitutional purpose: national defense. Before long, we may have cause to regret that shift.