Greg Gianforte, a Republican, was in a private office giving an interview when Guardian newspaper reporter Ben Jacobs went into the office without permission, Gianforte campaign spokesman Shane Scanlon said.
Jacobs "aggressively shoved a recorder in Greg's face, and began asking badgering questions" before being asked to leave, Scanlon said in a statement.
Gianforte asked Jacobs to lower a phone that being used as an audio recorder, then tried to grab it, the campaign said. Scanlon said Jacobs then grabbed Gianforte's wrist and both apparently fell to the ground.
Jacobs tweeted that Gianforte broke his glasses and is heard telling the candidate in an audio recording that the newspaper posted. In the recording, Gianforte can be heard saying that he was "sick and tired of you guys" and to "get the hell out of here."
The Gallatin County Sheriff's Office said it is investigating allegations of an assault involving the wealthy Bozeman businessman.
Jacobs, who was taken to a Bozeman hospital, could not be reached for comment by The Associated Press, and authorities did not provide any other details about the altercation.
The allegations come as Gianforte and Democrat Rob Quist made their final appeal to voters ahead of Thursday's special election to fill the state's seat in the U.S. House. Ryan Zinke resigned to join Trump's Cabinet as secretary of the Interior Department.
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