..."It is the easiest thing in the world to hook a small piece of explosive to a drone, and send it over an event," Kent Moyer, president of World Protection Group, a California-based private security firm, told Business Insider.

When it comes to protecting dignitaries, or stadium events such as sports and concerts, "nobody is really doing countermeasures against drones," said Moyer.

In fact, the Secret Service has established drone-free zones that prohibit flights within a 30-mile radius of presidential speaking engagements. The Secret Service also jams drone signals near the White House.

Nonetheless, the 20-year-old gunman who wounded Trump at a campaign rally in Butler, Pennsylvania on July 13 used a drone to scan the site just hours before he climbed the roof of a nearby building with a rifle. The FAA did impose restrictions on aerial drone flights for about two hours around the time of Trump's speech, though it is unclear whether jamming was in effect. But given a litany of security foul-ups that day, such as failure to secure nearby rooftops, and lack of coordination between the Secret Service and local police, there is ample reason to doubt whether the rally was drone-proof.

Assassination by drone is hardly new, at least for militaries and spy agencies. The US, Britain, Israel and other nations have done it for more than two decades, using larger drones such as the $30 million MQ-Reaper, armed with laser-guided missiles filled with explosives or even sharp metal blades that shred the target. But the danger now is that an insurgent or extremist can weaponize a $300 drone and strike a person within a half dozen miles with little warning.

Despite the proliferation of small drones in private hands, including terrorist groups such as Islamic State, they have not really been employed for non-state-sanctioned attacks on public figures. But the omens are there, notably in 2018, when Venezuelan president Nicolás Maduro survived an attack by explosive drones while giving a speech in Caracas....

As for the shooter: Routh has a long history of making political statements on X. He appears to have previously supported Trump before moving towards the Democrats. In a self-published book about the Ukraine War, he wrote about visiting the country and becoming disillusioned with its chances of defeating Russia. At that time, he worked with Ukraine's International Volunteer Center to recruit U.S.-trained Afghan fighters to join the effort. In the book, he described Trump as an "idiot" and a "buffoon."

He repeatedly posted on X in support of President Joe Biden and Vice President Kamala Harris, claiming that "democracy is on the ballot." In June of 2020, he reflected on his former support for Trump, writing: "While you were my choice in 2106 [sic], I and the world hoped that president Trump would be different and better than the candidate, but we all were greatly disappointment and it seems you are getting worse and devolving. I will be glad when you gone."

Routh apparently visited the nation's capital last year to advocate on Ukraine's behalf. The New York Times interviewed him while he was in the city, and he posted a picture of himself in front of the Capitol on LinkedIn.

Long before he is thought to have trained his guns on Donald Trump, Ryan Routh tried to tout his warrior skills in Ukraine as a volunteer with the country’s International Legion.

The unit was created by Volodymyr Zelensky, the Ukrainian president, in a bid to recruit ex-Western soldiers to Kyiv’s defence, and drew thousands of applicants in the war’s opening months.

However, far from all were battle-hardened Paras or US Delta Force members. The Legion also attracted no end of Walter Mittys, fantasists and self-publicists.

Ukrainian military recruiters appear to have spotted almost immediately that Mr Routh, who had a long criminal record, was not promising material.

According to an interview that he later gave to the Financial Times, he was rejected for service when he first reported to a Legion office on the Polish border at the war’s outset.

“They said: ‘You’re 56, you’re old and you have no experience’,” he told the paper. “So why don’t you recruit and coordinate?”

If that is what they told him, they probably intended him doing so having returned himself safely back to the US. Undeterred, however, Mr Routh continued on to Kyiv, where he became a familiar – if less than welcome – face on the Legion’s fringes.

There were many such cranks in Kyiv at the time, latching on to the war to pose as international men of action and boasting of high-level contacts in the Pentagon or CIA.

Regular Legionnaires did their best to avoid them, referring to them variously as “Call of Duty Warriors”, “Volun-tourists” and “Screamers” – the latter a reference to their reaction if coming under fire.

But there was little to stop them promoting themselves on social media, as Mr Routh did prolifically, claiming to be an active recruiter for the Legion ranks.

“Any gender, any age, any skill level to no skill level,” he claimed to Newsweek in 2022. “Yeah, if you wanna fight, come and see me and I’ll put you in a unit so you can go fight.”

Mr Routh, who claims to have had contacts in the Middle East, caused the Legion particular problems by attempting to recruit volunteer soldiers from Afghanistan and Syria, who would be unlikely to be admitted to Ukraine because of security concerns.

“He was never in Ukraine in any official capacity – he simply decided that he was going to come here and save the day himself,” a Ukrainian military source told The Telegraph. “I was in contact with him multiple times to request to him that he stop his activities, most of which were bizarre and alarming.”

One former Legion official told The Telegraph: “He was called out a number of times by Legion people and told to stop his shenanigans, but that didn’t seem to stop him. He was mostly quite eccentric. I could smell a mile away that he was full of s---.”

The military source added that because of the “chaos” during the first months of the invasion, it was easy for foreign self-publicists to make false claims that they were acting in an official capacity.

While Mr Routh probably had “good intentions”, he had also caused security problems for the Legion by posting details on his website of foreigners who had enlisted.

“He was trying to get involved in internal matters as well,” the source added. “He sent me messages saying: ‘Oh, guys in this unit are not happy.’ And I said: ‘Listen, they have a chain of command... there is a way to report things.’ I don’t think he was ever completely stable.”

Mr Routh also became a regular fixture in Kyiv’s Independence Square, where he erected his own makeshift memorial to the country’s war dead.

He would also hand out unofficial flyers offering $1,200 to anyone who took up arms against Russia. Eventually, his presence appears to have tested the patience of the Ukrainian authorities – who, according to the FT, ordered the memorial to be taken down.

The Legion is understood to have been at the point of requesting his removal from Ukraine altogether when he then left of his own accord.

Aware that Trump – not a noted champion of Kyiv in the war – might soon be back in the White House, Legion sources have stressed that they in no way approve of Mr Routh’s subsequent assassination plot. On said: “Disregarding political alignments, we would of course never condone this.”

That, however, may not be the only headache Mr Routh has left for Kyiv. According to the FT, after his makeshift memorial in Kyiv was taken down, he started a nearby Flags of the Fallen garden, where small paper flags are planted to remember Ukrainians who died in the war.

The flag garden is now home to thousands of flags and has become something of a landmark in Independence Square.

Much as the Kyiv authorities may not wish to remove it, they may not want to preserve something started by Trump’s would-be assassin, especially should Trump go to Kyiv next year as president.