On Wednesday, General Pierre de Villiers, resigned as Chief of the French General Staff. The top officer in the French military, de Villiers' resignation has shaken France's political establishment, because it's clear why de Villiers left his office.

He was furious with President Emmanuel Macron's plan to cut defense spending by 2.6 percent in 2017.

It's a justifiable concern. While campaigning for the presidency, Macron had pledged to reach the NATO target of 2 percent spending on defense (as a percentage of GDP) by 2025. And while he might yet do so, this year's cut is an obvious step in the wrong direction. And with thousands of French forces actively deployed against terrorist groups in Africa, and on peacekeeping operations around the world, this cut comes at a bad time.

As concerning is where Macron's cuts are being focused: the military equipment budget.

That's a problem because equipment procurement is the key to building a stronger warfighting capability. If soldiers cannot board aircraft to get to the fight, and cannot rely on helicopters, jets, and intelligence gathering platforms in the fight, they will be less effective.

Unfortunately, at present, France has an inadequate ability to move personnel and equipment such as tanks and armored vehicles at short notice and in large quantities. To address this deficit, the Fifth Republic needs more heavy-lift aircraft. But the longer Macron delays purchasing these capabilities, the more expensive it will be to do so. That's because of contract penalties that defense firms must be paid to keep their production lines cycling.

What's sad here is that France has traditionally been strong on equipment budgeting. According to NATO figures, in 2016, 24.5 percent of France's defense budget was spent on equipment. That share is significant and positive, and sits just behind the U.S. equipment share percentage of 25. The positive note stands especially strong in the context of too many NATO members spending outsize portions of their defense budgets on personnel.

Now the NATO tick mark next to France's name will be replaced with a cross.

Still, Macron does deserve some credit for one thing.

For all his strengths, of which there are many, General de Villiers was wrong to openly challenge Macron's authority. And he did so explicitly, complaining in a recent meeting with parliamentarians that Macron's defense cuts were an attempt to "f—k" him.

There can be no excuse for such conduct in a civilian democracy. As MacArthur had to learn from Truman, and McChrystal from Obama, whatever the rights and wrongs of a situation, the chain of command must always end with the democratically-elected government.

De Villiers rightly sought to protect the defense budget and the capabilities it affords France's defense. But he forgot the need to air his concerns only in private.

He was right to resign.