Biden to the country: 'Everyone's responsibility to lower the temperature of politics'

Meanwhile, security measures have been tightened around the convention and election-related events, with an increased presence of armed agents. Biden had previously promised a similar tightening and a review of all Secret Service security protocols. Strong controversy erupted over the security failures at Trump's rally and Biden pledged swift independent examinations of the incident.

The FBI is investigating to shed light as quickly as possible on the profile and above all the hitherto obscure motives of the 20-year-old man who attempted to assassinate Trump in Butler, Pennsylvania, an investigation that could prove crucial in the face of a nation in shock and to exorcise risks of escalating political violence. The attack, a sign of urgency, is being treated as an assassination attempt and an act of domestic terrorism mobilising every resource.

The sketch of the shooter remains full of shadows. The only certainty, according to the authorities, is that he acted alone and no clues have emerged linking him to accomplices or groups. Beyond that, what emerges from investigators and rumours so far is a portrait to be completed. Thomas Matthew Crooks had grown up and lived a few kilometres from Butler, at his parents' home. In a suburb - Bethel Park - of 34,000 residents, mostly white and middle class. Crooks worked as an assistant in a rehabilitation centre for the elderly. His parents are therapists. No criminal record, no history of mental disorders or ever having been under observation by the authorities. His online presence also appears to be very limited: an account on Discord, a gaming site controversial in the past for the presence of white supremacists, but Crooks would rarely use it and never for political discussions or ideas. He was wearing, at the time of the shooting, a T-shirt from Demolition Ranch, a site dedicated to weapons and explosives.

No manifesto left by the bomber has come to light so far. When it came to politics he was registered with the Republican party, but in 2021 he had also made a donation to a liberal group. He belonged to a shooting club. Former classmates in high school, where he had won a prize for science and mathematics, described him as having generally conservative views but above all as taciturn and reclusive, often bullied and often wearing camouflage or hunting clothes.

As for the weapons used, the rifle had been bought by his father, of libertarian faith, legally six months earlier. In his car were also found materials that could potentially be used to make bombs, which were however described as 'rudimentary'. Everything, including the shooter's mobile phone, was sent to the FBI's Quantico laboratories for analysis.

The dynamics of the attack, according to the latest reconstructions, have something of the rocambolic about them. The shooter allegedly climbed onto the roof of a shed near the rally, spotted by some spectators who had alerted local police officers. However, a policeman who had arrived on the roof allegedly fell when Crooks pointed his gun at him. Crooks then fired perhaps eight shots towards Trump and the crowd before being neutralised by Secret Service snipers. It is unclear why that roof had not been secured.

Fears about the future are compounded by the realisation that political violence and even attacks on presidents are not new in American history. President Ronald Reagan survived a shooting and so did Theodore Roosevelt as a candidate. Robert Kennedy was killed during his campaign and the list of presidents killed includes Lincoln, Garfield, McKinley and John Kennedy. Senators, congressmen and local authorities were repeatedly the victims of attacks.

In the Trump era, far-right violence has actually been the most frequent so far. Of 14 deadly attacks since 6 January 2021, when Trump supporters stormed Congress to keep him in power, 13 have been traced by authorities to this matrix. During Trump's rallies, the use of violent and apocalyptic slogans has been frequent to date.Polls have reflected a country not only polarised but also more prone to consider or imagine violence as a political method. Specialist firm Marist found that 47% of Americans believe they will see a civil war in their lifetime. And other recent surveys have seen 11% justify violent acts in support of a Trump return to the White House and, in general, 21% view them as legitimate in support of a cause.