POWER corrupts, goes the old saw. Yet Donald Trump’s presidency is the opposite case. It reflects the still-dumbfounding reality that one of the world’s oldest democracies elected a fully formed rascal to its highest office. Mr Trump did not even try to hide his designs. He promised to run the country as he ran his family business, which would logically mean nepotistically, autocratically, with great regard for his personal interests and little for the rules. And so he has.

The president has bent anti-nepotism laws to put his daughter and son-in-law in the house whose first occupant, John Adams, hoped only to “do a little good”. He has retained his business interests and cloaked his finances in secrecy. He has spent a third of his time as president at his commercial properties. He persists in claiming to have or to deserve sweeping powers over Congress, the judiciary and the constitution no matter how often he is reminded that he does not. His example permeates his cabinet of grifters. Ben Carson’s $31,000 dining set, Ryan Zinke’s secretarial flag, Scott Pruitt’s 18-man security detail, and private jets all round, were imitations of Mr Trump’s greater vanities.

Only after Mr Trump has left office will a proper accounting of the damage he has done be possible. Yet the fallout from an FBI raid on the offices of his personal lawyer, Michael Cohen, on April 9th could go some way to determining the extent of it. The raid appears to have sent Mr Trump hurtling towards the head-on collision with the rule of law that always seemed likelier than a trade or shooting war to define his presidency.

No one, save Mr Trump, represents the president’s tarnishing of American democracy more than Mr Cohen. An aggressive operator whose duties as a lawyer for the Trump Organisation allegedly included paying off his boss’s mistresses and threatening journalists (“I’m warning you, tread very fucking lightly, because what I’m going to do to you is going to be fucking disgusting,” he reportedly told one from the Daily Beast), he became the Republican Party’s national deputy finance chairman last year. He was by then known, as an adviser to Mr Trump’s campaign, for essaying the same tactics in politics that had earned him the nickname “Trump’s pit-bull”.

Asked in a memorable interview on CNN why his boss was trailing in the polls, Mr Cohen assumed a blank, show-me-the-evidence expression, and refused to accept the premise of the question. “Says who?” he kept repeating, even after it was put to him that the polls said so. It was an exhibition of Trump-style reality denial without the showmanship, as inept as it was cynical. The same can be said of Mr Cohen’s role in the intrigue that appears to have led the FBI to his Manhattan hotel room, residence and law office. It concerns his efforts to buy the silence of Stormy Daniels, a retired porn star, a couple of weeks before Mr Trump’s election, and then cover his trail.

Compared with the allegations of collusion between Team Trump and Russian election-hackers being investigated by Robert Mueller, this may seem trivial. Mr Cohen was within his rights to pay Stephanie Clifford, as Ms Daniels is properly known, $130,000 to keep quiet about having allegedly bedded Mr Trump. The legal difficulty for Mr Cohen concerns his subsequent claim to have done so with his own money and without Mr Trump’s knowledge. It is reported that he could have broken banking laws, by raising the money on false pretences; or that he could have broken campaign-finance laws, by failing to declare it as a benefit to Mr Trump. Such transgressions are potentially serious, yet rarely prosecuted. The scandal has nonetheless assumed an outsize importance for two reasons that go beyond Ms Clifford’s effectiveness in promoting it.

First, it has been billed as an early test of whether Mr Trump can be held to account. The Justice Department would not have sanctioned the raid, given the sensitivities involved, without strong grounds to suspect wrongdoing. It is hard to imagine Mr Cohen breaking the law on his boss’s behalf without his knowledge. Second, even if he did, Mr Trump may be in trouble, because rolling up Mr Cohen could help Mr Mueller gain a better understanding of the president’s private affairs.

Bye bye bagman

The FBI raid was launched partly on the basis of information provided by the special counsel. It is expected to furnish him with fresh documentation of Mr Trump’s financial and other arrangements, opening up new vistas of potential inquiry. If Mr Cohen is found out to be in serious jeopardy, Mr Mueller, who has already struck plea deals with three Trump campaign advisers, might even try to turn Mr Trump’s self-declared consigliere, provided the president does not pardon him first. In short, if Mr Trump has crossed serious lines, related to the Russia probe or otherwise, the chances of him being held to account, one way or another, appear to have risen. His frazzled response to the raid seemed to confirm that. He called it a “disgrace” and “an attack on our country” and warned, more aggressively than he had previously, that he might try to sack Mr Mueller.

It is more important than ever to prevent that. Because the Mueller investigation, as the related raid on Mr Cohen has just underlined, is about something even more important than the sanctity of elections. The probe was launched by the Justice Department, as a defensive measure, after Mr Trump sacked his FBI chief James Comey: its unwritten mission is to ensure the wheels of justice remain free of presidential interference. As the investigation into Mr Trump gets broader, that has never looked more necessary or more imperilled. So this presents the Republican congressmen who alone could pass legislation to protect Mr Mueller from Mr Trump’s mooted attack with a choice. Either they can stand with their party’s elected champion, or they can stand for the rule of law. It seems they can no longer do both.