Demands were mounting on Sunday for Donald Trump to receive protections on a level with a sitting president after a would-be assassin was narrowly foiled from carrying out what the FBI is investigating as an attempt on the life of the Republican nominee, the second against him in as many months.

Joe Biden on Monday said he believed the Secret Service – which has been plagued by staff shortages – needed more resources.

The president said “thank God” Trump was OK, before adding: “One thing I want to make clear [is] the Secret Service needs more help. I think Congress should respond to their needs.

“I think they need some more personnel.”

Biden’s comments came as an internal report into the operational failures that preceded the earlier assassination attempt against Trump – in July – is expected to detail lapses in communication between the former president’s protective detail and local law enforcement charged with securing the perimeter around political rallies.

A suspect, Ryan Wesley Routh, 58, a pro-Ukraine activist from Hawaii who is registered to vote in North Carolina, was detained after a Secret Service agent spotted the barrel of an AK-47-style rifle poking through a chain link fence on the outskirts of Trump International Golf Club West Palm Beach.

The former president is estimated to have been 300 to 500 yards away when a Secret Service agent saw the suspect and fired at him.

The suspect fled and was later arrested speeding north from Palm Beach in his car.

Republicans were the first to call for additional security, which has already been improved since Trump was targeted at a rally in Butler, Pennsylvania, by Thomas Matthew Crooks, who was killed by a Secret Service sniper. The 20-year-old gunman in the earlier case, whose motives appeared to be opportunistic, shot the president in the ear while killing one bystander and wounding two others.

The former White House press secretary Ari Fleischer said the Secret Service should change its policy and treat Trump like he is an incumbent with a larger protective perimeter around him.

“Stop being bureaucratic,” he said on X. “Do what’s necessary.”

In a statement on Sunday, Joe Biden said he had ordered the federal government to continue ensuring the “Secret Service has every resource, capability and protective measure necessary to ensure the former president’s continued safety”. But the president’s statement did little to quell demands for more protections for Trump as he runs against Kamala Harris in the 5 November election.

The New York Republican congresswoman Claudia Tenney said it was inexplicable that there had apparently been a second attempted assassination, remarking: “President Trump needs the same, if not more, Secret Service protection than a sitting president.”

The US House majority leader, Steve Scalise, a Louisiana Republican, said that the Secret Service must up their level of protection of him to their full capabilities – including “expanding the perimeter”.

The congressman Nick Langworthy, another New York Republican, said that recurring political violence targeting Trump “is unacceptable and deeply un-American”.

“This is not who we are as a nation, and it cannot be tolerated under any circumstances,” Langworthy said.

Such reactions largely came after the West Palm Beach sheriff, Ric Bradshaw – whose jurisdiction includes Trump’s golf course – said security would have been tighter if the former president was in office.

But the debate over what level of security Trump should receive has clashed with protocol and demands on the Secret Service’s $3bn budget. About $1.2bn is allocated to protective services for the sitting president and his family.

But where the sitting president’s detail is supported by the military, Trump is assigned a far lighter detail tasked to work with local law enforcement.

Before the Butler shooting, the Secret Service repeatedly denied requests for additional resources and personnel sought by Trump’s security detail. Denials of those requests often cited staff shortages, leading to tensions between Trump advisers and the agency.

Failures of communication between the Secret Service and local law enforcement about closing off lines of sight contributed to Trump’s vulnerability in Butler, an internal Secret Service investigation reportedly showed.

After that assassination attempt, security around Trump was said to have increased. The homeland security secretary, Alejandro Mayorkas, in July said that his agency, which includes the Secret Service, was beefing up protection for Trump.

“The Secret Service enhanced former president Trump’s protection based on the evolving nature of threats to the former president,” Mayorkas said at a White House briefing.

But Trump’s frequent golf games have long been viewed as challenging because golf courses are open areas and often close to roads. He owns courses in Florida, New York, New Jersey and Scotland, as well as numerous other locations.

Early on Monday, Trump thanked his security detail for protecting him.

“It was certainly an interesting day!” Trump wrote on his Truth Social platform. He thanked the Secret Service and local law enforcement “for the incredible job done today at Trump International in keeping me, as the 45th President of the United States, and the Republican Nominee in the upcoming Presidential Election, SAFE”.

Harris commended the Secret Service on Sunday, too, and described herself as “thankful” that her opponent in the presidential race was safe. The vice-president also condemned political violence while reiterating Biden’s pledge to “ensure the Secret Service has every resource” necessary to protect Trump.