It is almost a Washington tradition that, sooner or later, a sitting president will face investigation by a federal special counsel or special prosecutor – the terms are interchangeable. In recent history, only Barack Obama has escaped this fate and that was not for lack of opponents accusing him of nefarious misdeeds.

Now it’s Joe Biden’s turn and wolves are once again baying at the door of the Oval Office.

At first glance, last week’s revelations that old, possibly outdated classified documents had been found at a thinktank where Biden worked after leaving the vice-presidency in 2017, and in a garage at his home in Delaware, may not seem such a big deal. But such a view fails to understand the way Washington works. Significant or not, the find has given the flailing Republican party a stick with which to beat the president and it has seized it with grateful alacrity.

A clutch of GOP-controlled committees in Congress has already launched a series of investigations, in addition to the independent special counsel inquiry ordered by Biden’s attorney-general, Merrick Garland. They want to know whether national security was compromised; whether Biden’s son Hunter – a longtime Republican target – had access to the files; and why the White House failed to admit their existence until forced to do so by a CBS TV scoop.

Crucially, Biden’s opponents are posing the classic Watergate questions: what did the president know, when did he know it and was there a cover-up? It’s a sad fact that whatever Biden says now or in the course of what are likely to be wearying, attritional months of testimony and hearings, many Americans will not believe him. The distrust that infects and distorts US politics can only be expected to deepen.

The distraction of attention from Biden’s agenda and achievements is one of many prospective negatives for the president. Another is the unfair, potentially disastrous conflation of his alleged wrongdoing with the ostensibly much more serious case of his predecessor. Donald Trump is accused of secreting hundreds of contemporary classified papers at his Florida home and refusing to hand them over.

Biden previously accused Trump of “irresponsible” behaviour, words that are now being thrown back in his face. Suggestions that the misplacing of the documents was a mere oversight or act of forgetfulness play into the hurtful Republican narrative of a senile, incompetent 80-year-old president.

Biden did not help himself by joking that his garage was a secure space because he keeps his classic Corvette car there. If the word “Corvette-gate” has not already entered the lexicon, it soon will.

The extent of the damage to Biden and the Democrats will depend in part on whether Trump, the Republicans and their Fox News boosters succeed in sustaining and widening the scandal. They will propagate lies, disinformation and conspiracy theories.

The White House will try to play down the affair. Yet if, for example, the special counsel discovers the documents – reportedly relating to Ukraine, Iran and the UK – are not merely historical but contain current, sensitive or embarrassing secrets, Biden could be in deep water, politically and legally.

It’s almost exactly two years since Biden took office. After a rough start, his fortunes have steadily improved. Inflation is sharply down, Covid is mostly over (unlike in China), Russia is losing in Ukraine, Democrats did better than expected in the midterm elections and Maga Trump-ism continues to divide House Republicans. An announcement of a Biden run for a second term had been expected soon. All these gains suddenly appear in jeopardy and all because of a few dusty boxes of files.