Both the Conservatives and Republicans have decided they are above the law

Liz Truss wants a halt called to the Commons investigation into whether Boris Johnson lied to parliament, now he is stepping down as prime minister. Asked at the latest Tory leadership hustings in Darlington whether she would vote to end the privileges committee inquiry, the foreign secretary replied: “Yes.”

As she pointed out, there is little prospect of such a vote taking place. Yet Ms Truss’s statement is deeply worrying. Of course, she has won some brownie points, and votes, in the election by contrasting her status as a “loyal member” of Mr Johnson’s cabinet with her opponent’s decision to resign as chancellor. Yet Rishi Sunak did not bring Mr Johnson down; it was all his own work.

It is true that Mr Sunak’s decision provoked the avalanche of resignations by 60 Tory MPs which brought the Johnson premiership to a sudden end. But he could by no means have been sure that would happen. His actions have undoubtedly damaged his prospects in the Tory race; at hustings events, grassroots Tory members have criticised him for “wielding the knife”.

There is nothing wrong with the party valuing loyalty. Yet Ms Truss’s readiness to scrap the investigation suggests she has learnt nothing from Mr Johnson’s downfall. Her remark will give succour to his remaining allies, who are doing their level best to discredit the committee’s inquiry even before it starts work next month.

Nadine Dorries, a Truss cheerleader who sometimes does her campaign more harm than good, has called the investigation a “witch-hunt” and a “Machiavellian process”. It is nothing of the sort: MPs approved it and its terms of reference without a vote in April.

The committee has an inbuilt Tory majority. That has not stopped Mr Johnson’s friends claiming its members cannot possibly treat him fairly on the grounds they may have criticised him in the past. Yet there is no reason to think they would be biased against the prime minister. One Tory member, Bernard Jenkin, who chairs the liaison committee of senior MPs, has rightly urged fellow Tories to stop their “sort of terrorist campaign to try and discredit” the privileges committee. Alberto Costa, another member, has complained about “appalling, abusive remarks” from some so-called Tory “colleagues”.

The allegation that Mr Johnson misled parliament over Partygate is no less serious because he is leaving office. The claims must be heard in full and in public for there to be any chance of restoring public trust in UK politicians. It is not good enough to dismiss Mr Johnson as a one-off; the rules he repeatedly ignored must be enforced. If he were let off the hook without an inquiry, a future populist prime minister might not be deterred from lying to parliament, which carries the possible penalty of being suspended from the House.

The UK debate mirrors one taking place in the US after the FBI’s dramatic raid on the home of Donald Trump in Mar-a-Lago, Florida. Mike Pence, his former vice president, has demanded that Merrick Garland, the US attorney general, give a “full accounting” of why the search warrant was carried out, expressing “a deep concern” over the “unprecedented” search. That is the same Mike Pence who on the eve of the 2016 presidential election welcomed the FBI’s investigation into Hillary Clinton’s use of a private email server as secretary of state. (He accused her of “double standards”, even though he used a private email to conduct business as governor of Indiana).

Other Republicans have gone even further over the raid at Mar-a-Lago, with one member of Congress, Marjorie Taylor Greene, saying: “Defund the FBI.” There was no recognition of the serious allegation the FBI is investigating: the former president’s potentially unlawful removal and destruction of White House documents.

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Like Ms Truss in the UK, the Republicans are playing to their base and trying to turn events to their advantage, even if that damages the wider political system. In the US, the raid might even provide an early launchpad for an attempt by Mr Trump to regain the presidency in 2024. (In the UK, Mr Johnson has not ruled out such a comeback and some allies talk up the idea, however fanciful it sounds.)

Neither Mr Trump nor Mr Johnson should enjoy immunity. Politicians cannot be above the law, or the rules designed to uphold vital standards in public life. As a former justice secretary, Ms Truss should know it. She presents herself as a “straight-talking” politician who means what she says and delivers it. Yet such platitudes will not restore public confidence in her party or politicians in general.

Worryingly, Ms Truss has refused to commit to filling the post of the independent adviser on ministerial interests, vacant since Christopher Geidt resigned over Mr Johnson’s contempt for the rulebook. She should pledge now to appoint a new adviser – with enhanced powers – as soon as possible if she becomes prime minister. If she is to succeed where Mr Johnson failed, Ms Truss will first need to sweep the stables clean.