Rene Boucher pleaded not guilty to misdemeanor charges that he attacked Paul while the lawmaker mowed his lawn. Initially, police said Paul had suffered minor injuries, but the senator later tweeted that he suffered six broken ribs and had excess fluid in his lungs, CBS News reported.
Neighbor Alicia Stivers said she saw Paul right after the incident.
"He was having trouble breathing and talking. He had lacerations on his face," Stivers told Kentucky's NPR station, WKU.
The two men, both doctors, are on opposite ends of the political spectrum, but neighbors insist the altercation was trivial and had nothing to do with politics.
Jim Skaggs, another longtime neighbor, told CBS News that "Both men have really nice lives, really nice houses."
"It does appear to be a one-sided attack, that to my knowledge Boucher has not denied. In fact, he just broke," Skaggs said.
Boucher appeared in court Thursday and his attorney said he is remorseful about the incident.
"He's deeply regretful. This -- I don't think this would happen again in a million years," Matt Baker said.
Baker said his client and Paul were talking when Paul was working in his yard, CBS News reported. But Paul's chief strategist called the attack a "blindside" and dismissed reports of a longstanding dispute, saying the two neighbors haven't spoken in many years.
"I think blindsided is a very unfair characterization," Baker told CBS News..
Paul has retained a personal injury lawyer and contends he was violently attacked.