A group of suspected drug users arrested in Denver this weekend with methamphetamine, guns and bulletproof vests made racist threats against Barack Obama but posed no true danger to the presidential candidate who arrives here later this week to accept the Democratic presidential nomination, federal authorities said Tuesday. The three men - all said to be high on methamphetamine when arrested - are the subject of an assassination investigation, but so far, authorities say, it appears they had no capacity to carry out any attack on Obama. "The law recognizes a difference between a true threat - one that can be carried out - and the reported racist rantings of a drug addict," US Attorney Troy Eid said. He said the men's plans were "more aspirational, perhaps, than operational." The three have been charged with drug and weapons offenses but not with threatening to assassinate Obama or with other national-security-related crimes. Obama will become the first black nominee for president by a major US political party at this week's convention. Eid insisted that the vague racist threats from the men would continue to be investigated. He said he did not know whether Obama had been briefed on the arrests or whether security plans would change for Obama's acceptance speech Thursday. An affidavit released by Eid's office Tuesday showed the investigation into alleged threats intensified with an unnamed female who was with the men - Tharin Gartrell, 28; Shawn Robert Adolf, 33; and Nathan Johnson, 32 - while they were doing drugs in a Denver hotel room last weekend. The woman told police the men were using a racial epithet to refer to Obama and saying he should not live in the White House. Johnson later told a federal agent that the men talked about assassinating Obama only because he was black, according to a federal arrest affidavit. Johnson said he also heard Adolf say that he wanted to kill Obama "on the day of his inauguration" and that he would "find high ground to set up and shoot Obama," the affidavit said. Eid said authorities determined there was no firm plot to harm Obama. Asked what else they could plan to do with the weapons, Eid said, "I don't know what they were for." "A bunch of meth heads get together, we don't know why they do what they do. ... People do lots of stupid things on meth," Eid said. "If you're talking about a true threat, there has to be some evidence they're not just talking about it or thinking about it, especially in a drug-induced state." Homeland Security officials say the biggest domestic terrorism threat to the presidential conventions would be a "lone wolf" _ someone who sympathizes with white supremacists and is inspired by racist beliefs, according to an Aug. 22 intelligence assessment obtained by The Associated Press. In an AP interview last week, the head of the Secret Service's Protective division said the white supremacist threat to Obama has been exaggerated. "I think that it's something that, at times, the media tried to make more of," Nick Trotta said. "We've always watched them, as we watch all the other groups." Gartrell was arrested after police in Aurora, a suburb east of Denver, stopped a truck that was swerving erratically around 1:30 a.m. Sunday. He had a suspended driver's license, and the truck was rented under someone else's name, said Aurora police Detective Marcus Dudley. Aurora police Lt. Bob Stef said police found two scoped rifles, two wigs, camouflage clothing, a bulletproof vest and two walkie-talkies in the truck. A search also revealed 4.4 grams of what police believed to be methamphetamine and three IDs in other people's names, Stef said. Johnson and Adolf were arrested at area hotels after police interviewed Gartrell. Adolf jumped out a sixth-story window when police arrived Sunday. He broke his ankle but tried to run before police found him a short distance away. Adolf was charged with possession of a firearm by a convicted felon, possession of body armor by a violent felon and possession of methamphetamine with the intent to distribute, according to a criminal complaint filed Tuesday in US District Court in Denver. Gartrell and Johnson were charged with simple possession of meth, meaning the amount involved was less than 5 grams, and Johnson also was charged with possession of a firearm by a convicted felon. Three senior FBI officials said that at least two of the men may have had white supremacist ties. The officials spoke on condition of anonymity because they were not authorized to discuss the case. A fourth federal official familiar with the investigation said an assassination attempt was unlikely. "The capability and their opportunity and what they had for their weaponry - I don't see that they would have been able to carry it out," the official said on condition of anonymity because the investigation is ongoing. Adolf was hospitalized and held on $1 million bond for several outstanding warrants involving drug charges. He was on the "Most Wanted" list of the Weld County, Colorado, sheriff's department for burglary, larceny, aggravated motor vehicle theft and other charges. Gartrell, who has no known address, was being held at the Arapahoe County jail on $50,000 bail on drug and weapons charges. The jail said he was due in court Thursday. Eid would not describe the woman who was allegedly doing drugs with the men or say whether she was charged with a crime. Law enforcers were also investigating whether the men were linked to vandalism shootings that targeted at least two federal buildings in Denver over the past two weeks. Windows were shot at the US Custom House and the US Military Entrance Processing Station on the same street in Denver's downtown Federal District. Additionally, a bullet was recovered from a Hertz rental car that was hit Aug. 15, and authorities are now looking to see whether it could have matched the guns seized from the men.