The FBI is not a perfect institution. Like all big federal agencies, it is riven by factionalism. Like all law enforcement professionals, FBI officials can be overzealous. But it is crucial to the functioning of the law. Many people who have made their careers at the FBI are feeling undermined by a president who has contempt for their work. Many of Trump’s recent tweets have assailed the FBI.

I await Mueller’s findings of whether the president broke the law in dealing with Russia and the fallout of the election. Only he has anything approaching the full picture. That’s why upholding the legitimacy of his investigation – and investigators – is so important.

As the Republicans continue their campaign to discredit the FBI, it’s important to remember a piece of history. Without Deep Throat, the Washington Post’s secret source, the Watergate scandal might never have been exposed. Deep Throat, we learned in 2012, was Mark Felt, the No2 official at the FBI.

The constitution owes him, and those who have followed in his footsteps, a giant debt of gratitude.