Gianforte became involved in an altercation with Guardian US reporter Ben Jacobs on Wednesday on the final day after campaigning after Jacobs asked him a question about the American Health Care Act, the plan to repeal and replace Obamacare.
Gianforte's victory is a boost for Republicans, who are anxious Trump's political stumbles and the unpopularity of the healthcare bill passed by the House will hurt their chances of holding on to a 24-seat House majority in next year's elections.
'Great win in Montana, ' he told a group of pool reporters as he strolled past them in the Sicilian town of Taormina, where this weekend's G7 summit is underway.
Indiana Rep. Luke Messer said he wasn't sure whether the incident would hurt or help Gianforte in Thursday's special election for the open House seat. He ended up winning the special election, but before that was determined, late-night hosts weighed in on the alleged assault.
By the time sheriff's deputies arrived, more than half of voters had already cast their ballots in the race due to the state's mail-in voting law.
"You just body slammed me and broke my glasses", Jacobs said.
A Fox News reporter who witnessed the attack described seeing Gianforte grab "Jacobs by the neck with both hands and slammed him into the ground behind him".
A newly elected USA congressman has apologised after allegedly assaulting a news reporter one day before the special election. Pence and President Trump recorded a robo-call for Gianforte.
While Gianforte felt compelled to apologize, some of his future colleagues in the House Republican caucus didn't seem to think it was necessary.
"Last night I made a mistake and I took an action I can't take back and I am not proud of what happened", Gianforte told the crowd.
But early indications suggest that Republican House leaders have no plans to move against Gianforte - particularly after he apologized in an election night speech.
Gianforte was considered the favorite heading into Thursday's election to fill the seat once held by Interior Secretary Ryan Zinke, but that was before the altercation with Jacobs on Wednesday.
Quist, who raised more than $6 million for his upstart bid, said the experience gave him insight into the economic struggles some people face. "The last guy that came in here did the same thing", the candidate is heard saying.