A group of Republican lawmakers are blaming US President Joe Biden, claiming his campaign rhetoric led to the attempted assassination of Donald Trump.

As of Sunday, nearly a dozen lawmakers have pointed fingers at Mr Biden and Democrats at-large for the shooting Saturday evening at the former president's rally in Butler, Pennsylvania.

Many are pointing to a comment from Mr Biden while on a private phone call with donors last week.

According to Politico, Biden said on the call: “I have one job, and that’s to beat Donald Trump. I’m absolutely certain I’m the best person to be able to do that. So, we’re done talking about the debate. It’s time to put Trump in a bullseye."

On Saturday, Mr Biden condemned the attack and called on Americans to denounce such violence. On Sunday, he ordered a review of security at the rally.

In the aftermath of the assassination attempt, the specific reference to "Trump in a bullseye" less than a week before, has led some Republicans to place the burden of the shooting in part on Mr Biden.

"Joe Biden sent the orders," Georgia Republican Rep. Mike Collins posted on X, formerly Twitter, in a response to a post about Mr Biden's comments to donors.

In another post, Mr Collins wrote "they attempted to neutralize the threat", responding to a separate graphic featuring the president's comments.

"Notice that after an attempted assassination of President Trump, the same people who wanted him prosecuted for telling his supporters to peacefully march to the Capitol on January 6 are not calling for President Biden’s prosecution after he said it was time to put President Trump in the bullseye after their debate," Collins wrote.

FBI officials identified the shooter as Thomas Matthew Crooks, 20, a kitchen worker from Bethel Park, Pennsylvania, who is a registered Republican.

A Secret Service sniper fatally shot Crooks after he fired at the president.

Sen. Marsha Blackburn, a Tennessee Republican, also referenced Mr Biden's bullseye comment in posts on social media.

"Just days ago, Biden said 'it's time to put Trump in a bullseye'. Today, there was an assassination attempt against President Trump," she wrote on X Saturday evening.

Ms Blackburn also criticized Mr Biden for not releasing a statement for the first hour after the shooting, calling his delay "unacceptable".

"Go to the Oval Office and address the American people. We do not settle our differences by violence," she said.

Mr Biden spoke Saturday night from his home in Delaware where he was spending the weekend. He condemned the assassination attempt and called on all Americans to denounce such "sick" violence.

"We must unite as one nation to condemn it. It's sick, it's sick," he said.

Mr Biden then left Delaware to return to the White House, where he addressed the shooting again Sunday afternoon. A national address from the Oval Office is planned for Sunday night.

The sitting president also spoke with Trump over the phone on Saturday night in a call that one White House official described as "good, short and respectful".

Republicans on the House Judiciary Committee took to social media in response to Mr Biden's bullseye statement, too, asking reporters in a post if they plan to delve into the president's comment to donors.

"That just happened," they wrote in a post after the attempted assassination.

Rep. Lauren Boebert, a Colorado Republican, told 9News on Saturday night that she believes "much of the rhetoric from the left has escalated to this moment".

"President Trump was literally put in a bullseye after the President of the United States, the sitting President of the United States, called for him to be put in a bullseye," she said.

When asked if she thinks Biden bears responsibility for the attempted assassination, she replied: "I do believe that Joe Biden is responsible for the shooting today."

Other Republicans pointed to Democrats' recent efforts to end Trump's Secret Service protection after he became the first president convicted of felony counts for falsifying business records related to hush money payments to an adult film actress.

Rep. Bennie Thompson, a Mississippi Democrat and ranking member of the House Committee on Homeland Security, introduced the legislation in April that several House Democrats co-sponsored.

Rep. Marjorie Taylor Greene, a Georgia Republican who blamed the media and several Democrats for the shooting in posts on X, posted a list on the social media platform of Democrats who co-sponsored the legislation.

"Pray for America. The left wants a civil war. They have been trying to start one for years. These people are sick and evil," she wrote.

Sen. J.D. Vance, an Ohio Republican, who is on Trump's short list of vice presidential picks, echoed similar sentiments blaming the left's rhetoric.

"The central premise of the Biden campaign is that President Donald Trump is an authoritarian fascist who must be stopped at all costs. That rhetoric led directly to President Trump's attempted assassination," he wrote on X.

Republican Sen. Tim Scott of South Carolina said Democrats and the media have "recklessly stoked fears", and called Trump and conservatives "threats to democracy".

"Their inflammatory rhetoric puts lives at risk," he also wrote on X.

Louisiana Republican Rep. Steve Scalise, the House majority leader who was shot at a practice for a congressional baseball game in 2017, said Democrats have fuelled "ludicrous hysteria" about Trump being re-elected.

"Clearly, we’ve seen far left lunatics act on violent rhetoric in the past. This incendiary rhetoric must stop," he said.