It looks to us like Lawrence Kudlow is off to a good start as President Trump’s new director of the National Economic Council — just in the nick of time. The markets are on edge because President Trump has started to impose on Communist China, and some of our other adversaries, the tariffs that as candidate he’d promised the voters he’d use. Standing in front of the White House yesterday Mr. Kudlow went on Fox Business Network to try to calm the waters.

Mr. Kudlow’s basic message is that if there’s a problem on the trade front, the blame belongs not to Mr. Trump but to Communist China. That’s a smart strategy on almost any issue one can think of, but on few more than trade. That didn’t seem to be enough for Neil Cavuto, who greeted Mr. Kudlow’s reassurances by saying: “This doesn’t sound like the same laissez-faire, hands-off, Larry Kudlow I’ve respected and admired all these decades.”

That struck us as a bit harsh. Not that we lack for enthusiasm for free trade. We cut our editorial teeth on the Wall Street Journal, which, like Mr. Kudlow, has been warning Mr. Trump from the start against protectionism. We’re an abiding fan of the brilliant letters to the editor by which the economist Donald Boudreaux makes a daily case against protection. We favor the free movement of goods the way we favor the free movement of capital — and labor.

We tend to view tariffs in the constitutional sense. The laying and collecting of them are, after all, among the first powers granted in the Constitution to Congress. They are enumerated in Article 1, Section 8. It begins by saying that the legislature shall have the power to “lay and collect taxes, duties, imposts and excises.” It also has the power to regulate commerce with foreign nations. Is it the position of Mr. Kudlow’s critics that duties and imposts are forever out of bounds?

We’re not the first editors flying the flag of the Sun to have asked this question. It once cataloged “reasonable protection for American industry” as among its causes (alongside constitutional government, sound money, economy in public expenditures, the rights and responsibilities of the states, free enterprise, and equality before the law and opposition to “indecency and rascality” and populism, socialism, communism, and “government extravagance”).

History teaches that there’s a fine line between reasonable protection and catastrophe. If that puts a premium on discretion, it seems to us that Mr. Trump has as much claim to that discretion as any president, and more than many, in that he took the tariff question to the voters and won a mandate. Mr. Kudlow is arguing that the tariffs imposed so far are the start of a process and a negotiation the goal of which, at least for our side, is lower barriers, freer trade, and faster growth.

By pressing Mr. Kudlow on this head, Mr. Cavuto has done him a kind of favor. If this is what Mr. Kudlow gets from a friend, after all, imagine what he is going to get from his enemies. The New York Times is no doubt already preparing pieces writing off Mr. Kudlow as one of those who has sacrificed his good name for the chance to serve in a Trump administration. Mr. Kudlow has the advantage of remembering all the guff he had to take for helping craft the Reagan program.