If there has been one unifying theme to Donald Trump’s campaign, it’s probably this: Throw the bums out.

Unfortunately, that is not exactly a concrete set of policy proposals, nor is it a coherent governing philosophy. Despite what you may learn watching “The Apprentice,” you can’t just fire your way to success.

Still, Trump seems to think there is no problem that can’t be solved through layoffs.

At Wednesday night’s Commander-in-Chief Forum, for example, NBC’s Matt Lauer asked the Republican nominee about his declaration that within his first 30 days in office, his “top generals” would submit a plan for “soundly and quickly defeating ISIS.” What use would that serve, Lauer asked, when Trump has said that he already knows more about the Islamic State than the generals do?

“Well, they’ll probably be different generals, to be honest with you,” Trump retorted, later adding that current personnel have led to “the worst and you could even say the dumbest foreign policy.”

Democratic presidential nominee Hillary Clinton and her Republican opponent Donald Trump answered questions on national security and foreign policy Sept. 7 during a “commander-in-chief forum” on NBC News. (Video: NBC News/Photos: Melina Mara/Post, Mike Segar/Reuters)

At no point did Trump provide guidance on what he’d be looking for in new military advisers — other than, of course, a public endorsement of Trump — or what his or their secret master plan for defeating the Islamic State should look like.

Just a few weeks earlier, Trump suggested he might soon be cleaning house in the country’s intelligence agencies, too. On Fox News, he said he didn’t trust the U.S. intelligence community and planned not to use “the people that are sort of your standards.”

It’s not just the national security apparatus that deserves to be purged, in Trump’s view. As president, he would also cleanse the entire executive branch of career civil servants appointed during President Obama’s tenure.

“As you know from his other career, Donald likes to fire people,” Trump adviser and New Jersey Gov. Chris Christie said while explaining the plan — which would require changing federal civil service law — during a closed-door donor meeting at the Republican National Convention, according to Reuters.

(On this objective, Trump could get beaten to the punch; if a January government survey is to be believed, 1 in 4 federal employees would consider voluntarily resigning if Trump were elected.)

Trump’s pitch to voters is a broader application of this “fire everyone and don’t ask questions about their replacements” philosophy. Your lives suck, he tells voters, which means the whole system deserves to be burned down, and replaced with . . . something terrific.

“Look at how much African American communities are suffering under Democratic control,” he said last month. “To those I say the following: What do you have to lose by trying something new like Trump? What do you have to lose?”

In Trump’s pitch, establishment equals bad, new guy equals good — regardless of what that new guy stands for.

At least Trump practices what he preaches. Within his own campaign, he fired and replaced two campaign managers over two months, each time in an apparent response to declining poll numbers. As proof of Trump’s claim that he hires only “the best people,” the latest all-star lineup includes an accused sexual predator and the man who presided over the leading forum of the racist alt-right.

But, hey, better the devil you don’t know than the devil you do, right? That’s the Trumpian worldview.

Truly, I get the throw-the-bums-out impulse. It makes intuitive sense to look at disappointing outcomes and decide that something, and someone, needs to change. But smashing an unsatisfactory status quo without thinking deeply about who or what will succeed it is hardly a recipe for success.

Life would be easier if clearing out the dead wood were the same thing as planting new seedlings, if trimming the fat were the same as building muscle, if firing your defensive coordinator were the same as having a dominating NFL defense. But, sadly, that’s not how life works.

Schools can make it easier to fire bad teachers, but that doesn’t solve the problem of figuring out how to attract more good ones. Failing companies can ax their lowest-performing staffers, but they still need to come up with a product people want to buy. And voters can replace an entire cadre of long-serving establishment politicians with tea party novices, but that doesn’t mean those novices will render Congress any less dysfunctional.

Trump may well be right that the American people deserve something better than the current economic and political state of affairs. But “something better” is not the same thing as “something else.” By all means, voters may have motive to throw the bums out; still, we ought to careful about what kind of new bums take their place.