unless this guy has a pattern of such behaviour, i suspect montanans will be somewhat forgiving of gianforte. i could be wrong. but his action looks to me to be the result of an accumulation of stress and weariness, a feeling of grievance about a recent Guardian article, plus the aggregation of inputs in one moment. an isolated, circumstantial event in which his anger and stress was building over days or weeks.
i kinda recognise those as stress-related symptoms and i suspect many Montanans will also.
i'd suggest a remedy of a month's vacation.
on the other hand, he lied about what happened and didn't apologise. so those things may lose him the election.