The Republican candidate in the nationally watched election on Thursday for Montana’s sole congressional seat has been charged with misdemeanor assault for allegedly grabbing a reporter by the neck and throwing him to the ground.

Voters decide in the special election whether Republican Greg Gianforte or Democrat Rob Quist will fill the U.S. House seat left vacant when Ryan Zinke resigned to join President Donald Trump’s Cabinet.

‘Aggressive exchange’

Mr. Gianforte, who has tried to align himself with Mr. Trump, defended himself as the criminal charge was announced Wednesday, saying the reporter — Ben Jacobs of The Guardian — was being aggressive and grabbed him by the wrist in their exchange at his campaign office. Mr. Quist has declined to comment on the charge.

The assault charge is a last-minute curveball in the race, which was partly seen as a referendum on Mr. Trump’s presidency. The majority of voters were expected to have already cast ballots through early voting, and it was unclear how much of an effect the assault charge would have on the election results.