US President Joe Biden has used the formal setting of the White House Oval Office to ask Americans to lower the political temperature and remember they are neighbours after a would-be assassin wounded Republican rival Donald Trump.

Trump’s shooting “calls on all of us to take a step back”, Biden said on Sunday (local time) in remarks of less than seven minutes.

Thankfully Trump was not seriously injured, he said.

“We can’t allow this violence to be normalised. The political rhetoric in this country has gotten very heated. It’s time to cool it down,” Biden said.

“We all have a responsibility to do this.”

Trump responded to Biden’s remarks within minutes, posting “UNITE AMERICA!” to his Truth Social account.

“In this moment, it is more important than ever that we stand United, and show our True Character as Americans, remaining Strong and Determined, and not allowing Evil to Win,” Trump wrote.

“I truly love our Country, and love you all, and look forward to speaking to our Great Nation this week from Wisconsin.”

That was shortly followed by Trump’s departure for Milwaukee for the Republican National Convention as scheduled. It is set to go ahead as normal from later on Monday (local time).

At the convention, he will officially be named the Republican candidate for the November presidential election, and will name his official running mate and vice-presidential candidate.

It came as a senior Federal Bureau of Investigation official said Saturday’s shooting was being looked as a “potential” domestic terrorism act, as well as an assassination attempt.

“At this point [in] the investigation, it appears that he was a lone actor, but we still have more investigation to go,” said Robert Wells, the executive assistant director of the FBI’s national security branch.

The suspected shooter has been identified as 20-year-old Thomas Matthew Crooks. He was shot dead by the Secret Service seconds after opening fire on Trump from the roof of a building about 140 metres away.

An AR-15-style semiautomatic rifle was recovered near Crooks’ body.

There are also multiple reports that explosives were found in Crooks’ car, which was parked near Saturday’s rally in the town of Butler.

One man, identified as Corey Comperatore, was killed during the incident while two others were seriously injured.

Comperatore, 50, of Sarver, Pennsylvania, was killed when he dived onto his wife and daughter to protect them from the hail of bullets.

‘No place for this’: Biden

Sunday’s speech was Biden’s third use of the Oval Office to comment on issues of major importance to Americans since he took power in 2021.

Biden’s appearance allowed him to demonstrate the power of incumbency, an important symbolic image as he battles some in his own Democratic Party who want the 81-year-old leader to step aside from seeking re-election out of concerns he lacks the mental acuity for another four-year term.

In October, he made a prime-time speech to comment on the Gaza and Ukraine conflicts, and in June 2023 he spoke when a deal was reached with Republicans to avoid a breach of the US debt ceiling.

Gun violence is a fact of life in the US. However, political violence is rarer.

Despite that, four US presidents have been assassinated and several escaped assassination attempts. Multiple presidential candidates have been shot, some fatally.

Biden listed some of the previous attacks on public figures across the country – including the January 6, 2021 attack on the Capitol by Trump’s supporters and the beating of former House speaker Nancy Pelosi’s husband.

“There is no place in America for this kind of violence. Any violence. Period. No exceptions,” he said.

Biden and his team are trying to chart a course for his campaign following Saturday’s shooting attempt on Trump, who Biden considers a threat to American democracy should he be elected on November 5.

The Biden campaign called off verbal attacks on the former president to focus instead on the future.

Within hours of Saturday’s shooting, Biden’s campaign had cancelled television ads and suspended other political communications.

“Tonight I’m asking every American to recommit,” Biden said.

“Hate must have no safe harbour.”

-with AAP