The 6 January insurrection, when supporters of former US president Donald Trump stormed Capitol Hill, is widely viewed as a seminal moment in the history of US democracy. Never before had the modern nation witnessed such an organised, violent attempt to overthrow the elected government. Never before, not even at the height of the Civil War, had the Confederate flag flown over the halls of Congress.

Yet last week, as the US marked the first anniversary of the thwarted insurrection, another significant turning point was reached. President Joe Biden, the lawful winner of the 2020 election and Trump’s principal intended victim, dropped what some call his Mr Nice Guy act. With gloves off, Biden came out swinging. It was about time.

Since taking office almost exactly one year ago, Biden has deliberately ignored Trump. He has rarely mentioned his predecessor by name. He has refused to engage with Trump’s insults, lies and unceasing propagation of the “big lie” – that Democrats stole the 2020 vote. Instead, Biden sought to reunite a divided, fractious nation, appealing to what he called our “better selves” and looking to the future, not the past.

It didn’t work. That is not to say it was not worth trying, nor that the effort should be discontinued: it should not. But in the intervening 12 months, Trump, egged on by cynical, unprincipled Republicans such as House minority leader Kevin McCarthy and far-right disruptors such as Steve Bannon, has not only not faded from view but, rather, he has emerged, strengthened, as Republican king-maker and his party’s leading 2024 presidential contender.

Trump’s bottomless mendacity, lacking any factual, legal or moral basis and flying in the face of numerous court judgments, vote recounts and electoral inquiries, has nevertheless persuaded a majority of Republican voters that Biden was not legitimately elected while seeding doubt in the minds of others. His poison corrodes America’s governing institutions and incites civil strife. Trump embodies a clear and present danger to US national security, stability and democracy. He must be stopped.

Biden’s 6 January speech appeared to unleash a new strategy to do just that. Trump, he said, was “holding a dagger” at the throat of American democracy. His “web of lies” could no longer be tolerated. Trump “rallied the mob to attack”, then did nothing to stop the ensuing lethal violence, Biden fumed.

The president’s sudden switch to direct confrontation entails obvious dangers. It plays to Trump’s agenda and ego, making him the centre of attention. The shift may also be indicative of political weakness. Biden’s approval ratings are low, his legislative agenda has stalled, the Democrats in Congress are split and the party is widely expected to lose Congress in November’s elections.

Yet Biden really had no choice but to go on the offensive. Trump and Trumpism’s world of “alternative facts” has had a free run for too long. To be defeated and debunked, it must be publicly and robustly challenged at every turn. Legal remedies, soft-pedalled until now by the justice department, must be pursued with renewed vigour and determination.

“The legal path to investigate the leaders of the coup attempt is clear. The criminal code prohibits inciting an insurrection or ‘giving aid or comfort’ to those who do, as well as conspiracy to forcibly ‘prevent, hinder or delay the execution of any law’,” veteran Harvard constitutional law expert Laurence Tribe wrote recently. It’s a widely held opinion.

The many documented actions of Trump and his circle in attempting to overturn the 2020 vote provide numerous grounds for criminal investigation and prosecution. Why is Merrick Garland, the attorney general, still dragging his feet? Biden can righteously rage. But the best antidote to toxic Trump’s dangerously lawless spree, and fears of civil war, is the law itself. Take him down – before it’s too late.