President Donald Trump is showing that it’s possible to preside over a period of peace and prosperity and still be notably unpopular.

Over the past several months, Trump has opened even more of a wedge between the largely benign material conditions in the country and his own political standing, which is precarious and appears to be sliding backward. This isn’t how it’s supposed to work.

Republican politicos believed, reasonably enough, that last year’s tax cuts would stoke growth and create a good-news backdrop for Republicans in the midterms. The substantive part of this theory has worked swimmingly, with headlines just over the past week about middle-class incomes increasing over $61,000 for the first time, blue-collar jobs growing at their fastest clip in 30 years, and small-business confidence reaching an all-time high.

The only flaw is that the drumbeat of good news has coincided, lately, with a drop in Trump’s numbers. In much of the recent polling, he’s dipped back under 40 percent.

He hasn’t done this with any spectacular misstep. What Trump has done, predictably, week after week, is mess up the easy stuff.

It’s not hard — through gritted teeth and insincerely, if necessary — to say the appropriate things about an American hero upon his passing.

It’s not hard to limit your tweets on the morning of Sept. 11, for just a few hours, to the topic of the anniversary of the attacks and leave commentary on a recorded cable TV show for some other time.

It’s not hard to avoid attacking your own attorney general in public, in an escalating fashion meant to inflict the greatest possible humiliation.

It’s not hard to avoid throwing around the word “TREASON” loosely or to muse about changing the libel laws to exact legislation retribution on your critics.

Granted, it’s harder to build a cohesive White House team, but it ought to be easy to exclude volatile C-list stars from your old reality show and generate enough coherence to stem nonstop self-serving, backbiting leaks (let alone attacks on you in anonymous op-eds).

Any president grapples with the fact that he can’t control events; Trump grapples with the fact that he can’t control himself. He has dispensed with, to paraphrase Edmund Burke, the decent drapery of the American presidency, the norms devoted to investing the holder of the office — whether he deserves it or not — with a certain majesty.

Trump just lets it all hang out. This is gratifying to his core supporters, even as it creates a wearisome cycle of ceaseless controversies.

It’s not as though any one thing — the Stormy Daniels affair, the Cohen plea deal, the security-clearance controversy, the Omarosa book, etc., etc. — is as consequential as it’s portrayed in any given news cycle, but one damn thing after another adds up.

Trump has an amazing ability, through the force of his personality and his mediagenic provocations, to blot out the sun. He wouldn’t be president without this quality. It’s just that, given the positive state of the country, less blotting and more sun are called for.

Some caveats: Presidential popularity means something different in the age of Trump. He won election in 2016 with a favorable rating below 40 percent in many polls, so a return to that level may be less debilitating for him than prior presidents.

It’s not as though he’s creating controversies in an otherwise placid environment. He is confronted with an inflamed opposition, an extremely hostile press corps and a wide-ranging, aggressive special counsel investigation.

Finally, it is still possible that garden-variety Republicans will find a way to distinguish themselves from Trump this year.

All that said, we might be at the peak of the business cycle, and yet the president who is presiding over the good times — and signed the tax package that has boosted the recovery further — isn’t enjoying their full political benefit.

An economic boom is a terrible thing to waste.

Rich Lowry is a syndicated columnist. He can be reached via e-mail at: comments.lowry@nationalreview.com.

Rich Lowry