DONALD TRUMP seems to think he can best every challenge by insulting the challenger. It worked splendidly during the presidential campaign. But America’s institutions are not political foes. As an investigation led by Robert Mueller into possible links between Russia and Mr Trump’s presidential campaign grinds on, the president has flung ever more insults in the direction of law enforcement. His actions risk inflicting great damage on the country he leads.

On Twitter, Mr Trump calls the former heads of the FBI and CIA, as well as an ex-director of national intelligence and Democrats on Congress’s intelligence committees, “liars and leakers”. He also claims that “Investigators of the FBI and the Justice Department have politicised the sacred investigative process in favour of Democrats and against Republicans.”

The trigger for this outburst is a memo written by Republicans on the House intelligence committee about the surveillance of Carter Page, an oil-and-gas consultant who became a foreign-policy adviser to the Trump campaign. The memo claims that the FBI and DOJ failed to disclose that “an essential part” of the evidence used, in October 2016, to obtain the warrant allowing them to monitor Mr Page came from a dossier compiled by Christopher Steele, a former British spy, whose research was funded by Hillary Clinton’s campaign and the Democratic National Committee.

The memo quotes Mr Steele saying he was “desperate that Donald Trump not get elected and was passionate about him not being president” and alleges anti-Trump bias elsewhere at the FBI. Mr Trump, who approved the release of the once-classified memo on February 2nd, claims that it “totally vindicates” him.

In truth Mr Page is just one part of a sprawling, complex investigation, which began not with him but, three months before he fell under surveillance, with George Papadopoulos, another lightly qualified foreign-policy adviser, who has since pled guilty to lying to federal investigators. The memo does not say that the FBI and DOJ relied entirely on Mr Steele’s evidence in applying for a surveillance warrant. It asserts that Andrew McCabe, a former deputy FBI director, told the House intelligence committee that “no surveillance warrant would have been sought” without Mr Steele’s dossier. Democrats on the committee say this is a distortion.

The memo does a poor job of explaining why Mr Steele should not be trusted. He ran the Russia desk for Britain’s foreign-intelligence service and provided solid intelligence for the FBI before. His objection to Mr Trump seems to have stemmed from his belief that the candidate had been compromised by Russian intelligence. That is not the same as political bias. The same could be said for FBI agents investigating the Trump campaign’s alleged ties to Russia. As for Mr Page, he had been on the FBI’s radar since 2013, when Russian intelligence tried to recruit him. The court found sufficient cause to renew the 90-day surveillance warrant three times.

Congressional Republicans have nonetheless rallied around the memo. Matt Gaetz, perhaps Mr Trump’s strongest supporter in Congress, said it showed “a systemic pattern of abuse” in the FBI and Justice Department. That is hardly surprising. As Asha Rangappa, a former FBI agent who now teaches at Yale University, notes, “For the people who were already convinced, the memo could have said, ‘I’m Jesus’ in purple crayon 50 times, and it would have proved that Mueller is wrong.”

Democrats on the House intelligence committee claim that Republicans cherry-picked evidence. They have written a rebuttal memo, which the president must declassify before it can be released to the public. Should Mr Trump do so, it probably will make little difference politically. Democrats will believe one version of the truth, Republicans another.

And the damage will have been done. The Republican version of the story portrays America’s chief law-enforcement agency—whose former director, James Comey, may have swung the election to Mr Trump when he publicly reopened an investigation into Mrs Clinton just days before the vote in 2016—as well as the DOJ, helmed by Mr Trump’s appointee, as nests of devious liberals plotting to take down the president. This untruth appears to have caught on. A Reuters poll released on February 4th shows that 73% of Republicans now believe the FBI and Justice Department are “working to delegitimise Trump through politically biased investigations.”

That suits Mr Trump perfectly. Firing Mr Mueller would be extremely risky. It could even remind congressional Republicans that they are members of an equal branch of government who took an oath to support and defend the constitution, not Mr Trump and his family. Muddying the waters is probably a more effective strategy. If anti-Trump bias pervades America’s federal law-enforcement bodies, why believe anything Mr Mueller says?

But that question has an obverse. If intelligence sources believe the president might reveal confidential information whenever he deems it politically advantageous, why tell America anything? “What the memo has done,” says Ms Rangappa, “is advertise that the FBI cannot protect you.” Israel is already reconsidering its information-sharing after Mr Trump blithely revealed classified intelligence to Russian officials. Other countries may follow suit—not immediately, of course, and not entirely, because they still need America’s intelligence and data-gathering. But when people with vital information have to decide between going to leaky America and going elsewhere, elsewhere may look increasingly appealing.