There has never been an hour in the history of the American republic like it. On Tuesday, separated by 230 miles and 60 minutes, in two courts, in two cases brought by two different prosecutors, a US president’s former longtime lawyer, Michael Cohen, and his ex-campaign manager, Paul Manafort, were found to be crooks: guilty of bank fraud, tax evasion and paying off a porn star and a Playboy model in violation of federal campaign-finance law. Then again, there has never been a president like Donald Trump.

Mr Trump is a self-aggrandising liar whose desire for riches, infamy and adoration appears insatiable. The father of the US constitution, James Madison, once said that if men were angels they would not need government. But what if government itself is possessed by a character like Mr Trump? That is the threat the work of the special counsel Robert Mueller has been uncovering.

Mr Mueller had his best day on Tuesday. Both Cohen and Manafort had been in Mr Mueller’s sights. Both were convicted on eight counts, although Mr Mueller had handed over Cohen to the New York attorney’s office to prosecute. It is not the end of the story for Manafort, who is scheduled to go on trial in Washington DC in September over his work in Ukraine. Neither has Cohen finished. In court he admitted under oath that he broke the law at the direction of the president. Cohen has a reason to cooperate with Mr Mueller – he can reduce his sentence if he assists in further investigations. No wonder Mr Trump took to Twitter recommending that his followers not hire Cohen.

We are now entering a critical and dangerous period of the Trump presidency. Until now Mr Trump has been a mostly performative autocrat. He has encouraged the idea that he will lock up opponents, but he has not done so. Mr Trump attacks the “fake news” media but he has not sent thugs to smash printing presses. Yet the net is closing in on Mr Trump and his family. Mr Trump could spike Mr Mueller’s guns by pardoning all those found guilty – though that move might itself constitute grounds for impeachment.

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It is clear that the president wants his justice department to dismantle the Mueller investigation. This month, his legal adviser Rudy Giuliani threatened to “unload” on Mr Mueller “like a ton of bricks” if the investigation isn’t wrapped up soon. But this is a risky strategy ahead of midterm Congressional elections, when the Democrats stand a decent chance of retaking the House of Representatives, and perhaps even the Senate. A misstep by Mr Trump could electrify the Democrat base. If the Democrats controlled both houses of Congress, they could rehire Mr Mueller as a “congressional” special prosecutor should the president fire him.

Mr Trump’s reshaping of the courts means that if the battlefield moves from the legislative to judicial arena, then the odds move in the president’s favour. Mr Trump will not voluntarily be interviewed by Mr Mueller’s team. He is daring the special prosecutor to issue a subpoena to force him to comply. If the judiciary is asked to intervene to force the president to testify, it is doubtful that the special counsel would prevail in the end. This would be especially true if Mr Trump’s supreme court nominee, Brett Kavanaugh, were on the bench. He has suggested that a sitting president should not be indicted and questioned whether the head of the executive can be investigated by a special prosecutor.

US institutions were not designed to protect the public from a leader like Mr Trump. Principled politicians, judges and lawyers are needed to dig deep in the face of much resistance. The Watergate investigation took two years to play out. It brought down a president and sent dozens to prison. Mr Mueller has been going for 15 months. Watergate showed that the system could cope and that not even a president was above the law. Mr Mueller needs to be shielded to prove that the system can work as well as it did then.