Three men who authorities initially feared were plotting to assassinate Barack Obama at the Democratic National Convention are facing only gun and or drug charges, after the U.S. Attorney's Office deemed that there was insufficient evidence to charge them with conspiracy, making threatening statements, or other national security-related crimes.It's possible that additional charges could come later, since the investigation is continuing, but that is unlikely, said U.S. Attorney Troy Eid during a Tuesday afternoon news conference.Tharin Gartrell, 28, Nathan Johnson, 32, and Shawn Adolf, 33 were all arrested within hours after Gartrell was spotted driving erratically near Parker and Hampden in Aurora around 1:30 a.m. Sunday.Eid said the men were not serious about carrying out the threats."Please understand that the law recognizes a difference between what we call a true threat -- that's one that can actually be carried out -- and the reported racist rantings of drug abusers," Eid said. "The jargon for this sometimes is, 'It was more aspirational than operational.' In this particular case, there's insufficient evidence that there was any kind of plot or conspiracy."In the federal arrest affidavit, an agent with the Alcohol, Tobacco and Firearms Bureau writes that Johnson told a Secret Service agent, described only as SA Torres, that "Adolf had, in fact, threatened to kill Obama on a prior occasion ... that he wanted to kill Obama on the day of his inauguration and ... would specifically use a 22-250 sniper rifle."Special Agent Shane Abraham of the ATF goes on to write, "Johnson then told (SA Torres) there were no political reasons for wanting to kill Obama, the only reason is because Obama is black.""We will continue to check out anything related to this and the security of the people here. We live here. This is our community. We care a lot about what happens here. And we protect every person. So, I just want to say, with all due respect, we will continue to do that," Eid said.Gartrell was arrested near Denver with two rifles, a bulletproof vest, ammunition, walkie-talkies and suspected drugs. Federal officials say the other two men and a woman were apprehended a few hours later.In jail, Johnson was asked by a reporter if he felt there was a plot to kill Obama.Johnson said, "Looking back at it, I don't want to say yes, but I don't want to say no."Johnson was interviewed while being held in jail on felony drug possession. Johnson told the reporter he wasn't involved in any plot.A judge on Tuesday set Johnson's bail at $10,000 but he did not immediately post bond and remained in jail. He did not speak during a brief court appearance Tuesday morning, and jail officials said he was refusing other interview requests."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," an official close to the investigation said.But authorities don't doubt that Aurora police, who are on heightened security surrounding the Democratic convention in Denver, were right in contacting federal authorities with their suspicions.When Gartrell was stopped, he had a suspended driver's license, and the truck was rented in the name of another person, said Aurora police Detective Marcus Dudley.The address on his license listed a home in Centennial, Colo., but that is not his current address and police still do not know where he lives, Dudley said. At least one of the rifles in his truck had a scope and was stolen out of Kansas, he said.Later Sunday, federal agents arrested Johnson, 32, at a hotel in Denver. He was held on drug charges. A half-hour later, Adolf jumped from a sixth-story window when authorities tried to arrest him at a hotel in Glendale, police said.Adolf was hospitalized and was being held on $1 million bond for seven outstanding warrants involving drug charges. He had a handcuff key in one hand and a swastika ring on the other when he was arrested, a senior FBI official said.Dudley said Gartrell was being investigated for methamphetamine and firearms violations. Gartrell was being held at the Arapahoe County jail on $50,000 bail on drug and weapons charges. Gartrell was charged with misdemeanor domestic violence in 2005, but those charges were later dismissed, according to Colorado court records.The fourth person arrested was a woman described by federal authorities as the girlfriend of one of the men.Law enforcement officials 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 U.S. Custom House and the U.S. 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 on Aug. 15, and authorities are now looking to see if it could have matched the guns seized from the men.