‘We have people across this country who are scared to death,” New Jersey Gov. Chris Christie declared loudly at this week’s GOP presidential debate in Las Vegas.

Virtually the entire debate was based upon this premise. Which is understandable. Since the bloody Islamist attacks in Paris and San Bernardino, terrorism has shot up as the chief concern for most Americans, particularly Republican voters.

“For most of 2015, the country’s mood, and thus the presidential election, was defined by anger and the unevenness of the economic recovery,” pollster Fred Yang of Hart Research Associates explained upon the release of the latest NBC News/Wall Street Journal poll. “Now that has abruptly changed to fear.”

Only 34 percent approve of President Obama’s handling of the Islamic State, according to the poll, and more Americans are worried about terrorism than at any time since the aftermath of 9/11.

This abrupt change in the climate explains why Hillary Clinton is suddenly talking much tougher about terrorism and why the president is keen to get some good national-security photo-ops.

But I can’t shake the sense that the polls, politicians and my fellow pundits are mistaking a symptom for the disease.

We live in an anxious age. That anxiety runs like a river beneath the political landscape. Different news events tap into that river and release a geyser of outrage and fear. Right now, mostly on the right, it’s terrorism, but before that it was Mexicans illegally sneaking into our country. Sometime before that, there was the freak-out over Ebola.

One common explanation is that the economy is undergoing a profound transformation that is leaving a lot of people on the sidelines. It seems obvious there’s a lot of merit to this explanation.

But I don’t think economics explains everything. Seventy percent of Americans think the country’s on the wrong track. Many of those people are doing just fine economically.

No, I think the missing piece of the puzzle is the fact that Americans — on the left and right — think that the folks running the country have an agenda different from theirs. The left has a much richer vocabulary for such claims, given its ancient obsessions with greed and economic determinism. They see big corporations and the so-called “1 percent” pulling strings behind the scenes. (Watch literally any Bernie Sanders speech on YouTube to learn more.)

But while a great many people on the right also complain about crony capitalism and special interests, such concerns don’t get to the heart of the anxiety, at least not for conservatives.

Let’s go back to where we started. Christie says, “We have people across this country who are scared to death.” No doubt that’s true. But for a great many of them, I suspect, the fear isn’t so much a fear of the Islamic State but a fear that our own government, starting with the president, just doesn’t take terrorism seriously. We now know he was very late in taking the Islamic State seriously.

I suspect most conservatives think that if America marshaled the sufficient will to defeat the Islamic State, we’d make short work of it. Obama has no interest in such an undertaking. He reserves his passion for attacking Republicans or pushing his other priorities, such as climate change, which persistently remains a very, very low priority for most Americans.

But the president himself is a symptom. The whole system seems to have lost its mind. That there’s even a debate about whether security officials should be allowed to look at the social-media posts of immigrants is a sign that our bureaucrats have such open minds their brains have fallen out. We should have seen this coming five years ago, when we learned that Obama told the new head of NASA to make one of his top priorities outreach to the Muslim world.

Terrorism is a big concern, but this sense that the political system is unresponsive, unaccountable and operating on its own self-interested ideological agenda is bigger. It is the ur-complaint that explains everything from enduring outrage over the lies that greased ObamaCare’s passage to fury over illegal immigration, disgust over corruption at the IRS and VA, the immortality of the Ex-Im Bank and countless other outrages du jour.

The failure of credible politicians to address this anxiety created an opportunity for Donald Trump. At least he’s willing to say Washington is stupid.