GEORGE CONWAY, a successful corporate lawyer who happens to be married to Kellyanne Conway, one of President Donald Trump’s most trusted advisers, has for months been making discreet digs at the president on Twitter. He observed that Mr Trump’s tweets about his travel ban might imperil it in court. When the president said he might pardon Muhammad Ali, Mr Conway posted a link to the Supreme Court decision in 1971 that had cleared the late boxer of his conviction. But this week Mr Conway socked it to Mr Trump good and proper. In a cogent 3,500-word article he explained why a flagrantly partisan attack on the legal authority of Robert Mueller, enthusiastically trumpeted by the president, is utterly bogus.

The article (“The Terrible Arguments Against the Constitutionality of the Mueller Investigation”), which was published on Lawfare, an influential blog, appears to have been provoked by a tweet by Mr Trump on June 4th. “The appointment of the Special Counsel is totally UNCONSTITUTIONAL!” wrote the president of the respected investigator who is understood to be probing him for possible obstruction of justice and his campaign team’s many links to shadowy Russians.

Mr Conway suggested Mr Trump had latched onto an argument made by Steven Calabresi, a legal scholar who co-founded the Federalist Society, America’s leading organisation of conservative and libertarian lawyers, of which Mr Conway is a member. “Unfortunately for the president, these writings are no more correct than the spelling in his original tweet,” he wrote. (Mr Trump had spelled the word counsel, “councel” before correcting it). Mr Conway then proceeded to rip apart Mr Calabresi’s views, which have been published in the Wall Street Journal and elsewhere.

Mr Calabresi contends that Mr Mueller’s appointment violates the “appointments clause” of the constitution, which decrees that “principal officers” of the United States must be nominated by the president and approved by the Senate. Mr Mueller, appointed by the acting attorney-general, Rod Rosenstein, acts like a principal officer, argued Mr Calabresi, because he has no boss who supervises him. “Only a principal officer, such as a U.S. attorney, can behave the way Mr. Mueller is behaving”, he wrote. Mr Mueller’s work is therefore constitutionally “null and void.”

Rubbish, said Mr Conway. Mr Mueller, like US attorneys, is an “inferior officer” of the sort that need not be appointed by the president. In fact, Mr Conway pointed out, Mr Mueller’s office has less heft and authority than many US attorney’s offices. Extensive public records, meanwhile, prove what kind of an officer he is; he is “appropriately supervised and directed” by Mr Rosenstein. Mr Conway also pointed out that when Paul Manafort, a former Trump campaign manager, tried to dismiss the indictment against him on the grounds that Mr Mueller had overstepped his official remit, the United States District Court for the District of Columbia “squarely rejected this assertion”. It even said that Mr Mueller would have been remiss not to have investigated Mr Manafort.

“So not only does Mueller have a boss, and not only is the boss keeping tabs on Mueller, but, according to this judicial decision, Mueller is also faithfully following his boss’s orders”, concluded Mr Conway.

Of course, Mrs Conway is not her husband’s keeper. But still, it is striking to read such a powerful shredding of one of Mr Trump’s attack lines from the spouse of one of his most slavish defenders. Mrs Conway is so fond of using alternative facts to defend her boss that she was briefly barred from CNN. Her husband’s tweeting and writing has not made her life easier. Mrs Conway recently accused Dana Bash, a journalist with CNN, of trying to “harass and embarrass” her when she quizzed her about her husband’s views.

In fact Mr Conway’s article is mostly valuable as a scandalously rare effort by a Republican lawyer to speak up for the rule of law against Mr Trump’s assault on it. His recent claim to have an “absolute right” to pardon himself and his repeated claims that the Mueller investigation is a “witch hunt” have drawn hardly any notable pushback from members of the Federalist Society. And it is depressingly obvious why this is so. During his campaign Mr Trump promised that his judicial nominees would “all be picked by the Federalist Society”, and he has largely kept that promise.

Mr Conway, who was head of the Federalist’s Yale Law School chapter as a student, appeared to call its members out on their complacency about the president’s behaviour. It wasn’t surprising, he wrote, to see the president, no lawyer himself, tweet about a “meritless legal position”. But while lawyers may make “inventive and novel arguments” to aid their clients, these should always be "well-grounded law and fact" even if they are incorrect. “The arguments against the special counsel do not meet that standard”, Mr Conway wrote.

“Such a lack of rigour, sadly,” he added, “has been a disturbing trend in much of the politically charged public discourse about the law lately, and one that lawyers—regardless of their politics—owe a duty to abjure”.