MILWAUKEE (Reuters) - Their presidential candidate had just narrowly escaped an assassination attempt, a bullet grazing his ear on Saturday from an AR-15-style semiautomatic weapon - a rifle frequently used by mass shooters in the United States.

Yet in interviews with 12 Donald Trump delegates at his Republican Party nominating convention in Milwaukee, none advocated for limits or bans on assault rifles, raising the legal age to buy a gun, or even more robust background checks.

The delegates were dead set against any type of reform to America's gun laws.

Most viewed even mild measures, such as expanded background checks, or raising the legal age to buy an assault weapon to 21, as infringements on the U.S. Constitution's Second Amendment, which grants citizens the right to own guns.

Instead, the delegates said any gun-related reforms should focus on funding better mental health support for troubled citizens, a standard Republican position. They blamed gun crime and gun massacres - including the assassination attempt on Trump - largely on mental illness and weapons falling into the wrong hands.

U.S. law enforcement officials are still trying to determine why Thomas Matthew Crooks, a 20-year-old nursing home aide, shot at Trump at his election rally in Pennsylvania on Saturday. Crooks was shot dead in the attack, which the FBI said was being investigated as potential domestic terrorism.

More effective mental health services are the key to spotting potential shooters and getting them help before they carry out a gun crime, the delegates interviewed said.

"It's all about mental health," said Will Boone, a delegate from Montana. "The right to have a gun is enshrined in the Constitution. Once you start infringing on that, you'll start other rights being taken away."

Steve Kramer, from Georgia, said it was a "lie" that expanded background checks would help.

"If you look at most of the killings, someone stole the gun, so background checks wouldn't matter," Kramer said.

Between 1966 and 2019, apart from school shooters who mainly stole their weapons from family members, most people who committed mass shooting had bought their weapons legally, according to data compiled by the National Institute of Justice, a research agency of the Department of Justice.

The weapon used by Trump's would-be assassin was owned by his father, according to investigators.

The Republican Party has generally blocked attempts to reform gun laws, even after the massacre of 20 elementary school children in Connecticut in 2012 by a gunman armed with an AR-15 assault-type weapon and two handguns.

Efforts to pass universal background checks and an assault weapons ban were defeated by Republicans in the U.S. Senate after that school massacre.

During his 2017-2021 term, Trump tried several times to loosen gun laws, said Kris Brown, president of Brady: United Against Gun Violence.

Shortly after taking office he signed into law a bill that reversed an Obama-era regulation that made it harder for people with mental illness to purchase guns.

The Trump administration did ban bump stocks, an accessory that essentially converts a semi-automatic weapon into a machine gun. A bump stock was used in America's deadliest mass shooting, in Las Vegas in 2017, when a gunman killed 60 and wounded more than 400 people.

In June, the conservative-leaning U.S. Supreme Court lifted the ban on bump stocks.

In February, speaking to the National Rifle Association, Trump pledged to undo all gun-related restrictions enacted by Democratic President Joe Biden, whom he faces in the Nov. 5 election.

Matthew Rust, a delegate from Wisconsin, said he believed an armed citizenry is a deterrent to shooters. "When a perpetrator knows there may be law-abiding citizens that can defend themselves they are less likely to take action," Rust said.

(Reporting by Tim Reid and Helen Coster in Milwaukee, Editing by Ross Colvin and Howard Goller)

By Tim Reid and Helen Coster