“Assaulting the female campaign manager of the opposing campaign is disgusting and it has no place in our system,” campaign spokesperson Parker Briden said. “This mob behavior from the left is out of control. Encouraging violence, as many prominent Democrats like former Attorney General Eric Holder have recently done, is having real, dangerous consequences.”

Protesters in recent months have hounded GOP lawmakers and officials out of restaurants in chaotic moments caught on video. Holder was accused of fanning the flames for saying last week, "when they go low, we kick them," in a twist on former first lady Michelle Obama's famous slogan. Holder later said he wasn't advocating violence.

Democratic candidate Steve Sisolak's campaign and state party officials deny any connection to Stark.

A spokesman for American Bridge did not respond to Fox News’ request for comment. It's not clear whether he was on the job for American Bridge during the confrontation, but he works for the group, listing himself as a reporter for them on his LinkedIn page.

Stark also has a record of arrests while working for American Bridge. Stark was arrested on Oct. 28, 2017 for disorderly conduct at an event in Virginia while covering then-GOP gubernatorial candidate Ed Gillespie. He was found guilty of disorderly conduct in February of this year.

The incident with Zinke’s press secretary Heather Swift occurred in March at the Longworth House Office Building after a budget hearing before a House committee. Stark allegedly approached Zinke and reportedly “used his full body to push” Swift as she tried to leave the room. Swift, who called the incident “terrifying,” told police that she decided to press charges to help obtain a “stay-away order” against him.

It's not immediately clear if Swift has a lawyer.

“It’s shocking to me that anyone in this business, no matter which party or issue you’re working on, would keep someone on their payroll who has been consistently arrested for violence,” Davison told Fox News. “This is a terrifying incident.”

American Bridge was founded in November 2010 by David Brock, who also founded liberal watchdog group Media Matters.

The group’s largest donor is liberal billionaire Soros, who donated more than $2 millionbetween 2015 and 2016. Soros is still involved with the group, most recently donating $300,000 in February,  and $80,000 last year.

The Associated Press contributed to this report.