Bernville District Judge Andrea Book issued the verdict against Sen. Bob Mensch, R-Montgomery, after a hearing that lasted nearly 2½ hours.
Mensch faces a maximum sentence of 90 days in jail and a $300 fine, although Berks County Assistant District Attorney James Goldsmith said he would not recommend incarceration.
Testifying under oath, Mensch and the other motorist, Brian Salisbury, offered sharply conflicting versions of the events of March 9 that resulted in the charge against the senator. Mensch denied displaying any sort of weapon and presented a string of character witnesses, including a Roman Catholic priest and two police officers who described him as a law-abiding man.
Both men agreed that the encounter occurred late in the afternoon along an eight-mile stretch of the interstate in Berks County and ended at a gas station just off the highway.
Salisbury, 55, who commutes from his home in Easton to his job in Harrisburg, said Mensch's vehicle came up from behind while Salisbury was passing a tractor-trailer and began tailgating him.
When he pulled into the right lane after passing the truck, he said, Mensch passed him and then slowed down. As Salisbury's vehicle came alongside, Mensch displayed a black handgun in his palm at about lap level, Salisbury said.
"It was definitely a gun," he said, adding that he slowed down and called 911 to report the incident.
"It just scared me," he said. "I didn't know what was going to happen and I just pulled back."
Shortly afterward, both men wound up pulling into the same gas station, where Mensch filled his gas tank and Salisbury described the incident to police on his cellphone, they testified.
State Trooper John Wenrich, one of the troopers who pulled over Mensch after he left the gas station, testified that he observed a black pistol under a scheduling book on the passenger's seat and that another pistol was revealed when Mensch opened his glove compartment to retrieve his driving papers.
Mensch, 65, who has concealed-weapon permits to carry both guns, denied that he displayed any weapon that afternoon, suggesting that Salisbury might have seen him holding his cellphone.
Mensch, a former state representative who won a special election to the Senate in October, is a co-sponsor of a Senate-approved bill to ease legal restrictions on the use of deadly force in self-defense in Pennsylvania. The House has passed similar legislation.
The senator claimed Salisbury was "dallying" in the passing lane when Mensch approached from behind. The senator said he became frightened after Salisbury pulled into the right lane because he said Salisbury made "gestures with his hand" andtailgated him until they stopped at the gas station.
"I had no sense of what this man's intent was," he said.
Mensch acknowledged that at the gas station he took the black pistol from its box under the front seat and stuck it under his coat in the small of his back, but said he did so because he feared for his safety.
Defense attorney Rich Wagner told the judge that Mensch did nothing wrong because he never used the gun in a threatening way.
"It was never raised. It was never pointed," he said.
Goldsmith, however, said state troopers corroborated key parts of Salisbury's version of events, and his description of the black gun undercut the defendant's contention that he was not displaying a weapon.
"That's one heck of a lucky guess," he said.