I spent the better part of my working life close to the mechanics of commerce — setting type for advertisements, discounting bills of exchange, fretting over the soundness of colonial paper. One lesson I took from all of it is this: the man who profits from a sale has no business setting its price. That is not a novel principle; it is the first rule any honest shopkeeper teaches his apprentice.

CNBC reports that President Trump purchased as much as $5 million in Axon Enterprise stock — Axon being the maker of Tasers and police technology — while the Immigration and Customs Enforcement agency, which answers to his administration, was pursuing a potential $220 million contract with that very company. Axon, the same report tells us, has ramped up its lobbying in Congress on federal law-enforcement technology as that negotiation proceeded.

I will not pretend to know the engineering of modern body-cameras or the precise terms of a federal procurement contract, for those are details beyond my era. But I know what a conflict of interest looks like, and I know that the public treasury is not a private trading account. When the sovereign — or the sovereign's officer — holds an equity stake in the company whose bid he is evaluating, every dollar the contract pays above the fair market price travels, in part, back into his own pocket. That is not commerce; that is a toll collected in secret.

The founders of this Republic — and I count myself among those who argued hardest for republican virtue — understood that public office must be insulated from private gain precisely because the temptation to confuse the two is irresistible to most men. We built disclosure requirements and conflict-of-interest rules into the architecture of self-government for the same reason we built checks and balances: not because we assumed every official was corrupt, but because we knew that unchecked power and private interest, left in the same room, will inevitably find each other.

Axon's lobbying campaign alongside this procurement, as described by CNBC, is the other side of the same coin. A company that sells to the government is entitled to make its case; that is legitimate. But when lobbying, procurement, and the personal portfolio of the deciding official all point in the same direction, the working taxpayer — the small farmer, the tradesman, the wage-earner — has no advocate at the table. She pays the $220 million and receives in return not only the equipment but also, as inference would suggest, a healthy return for the official whose thumb was on the scale.

A penny saved is a penny earned is, I confess, a maxim so often repeated that it has lost its edge. Let me offer a sharper one for the occasion: a conflict disclosed is not a conflict resolved. If you are a citizen who cares how your tax dollars are spent, demand — from your senator, your representative, any official who will take your letter — that no executive officer trade in the shares of any company actively seeking a federal contract under that officer's authority. That rule costs nothing to write and saves a great deal more than a penny.