Speaker of the House Paul Ryan (R-WI) answers questions from reporters at the U.S. Capitol.

House Speaker Paul Ryan on Thursday called on Republican Greg Gianforte to apologize after he was charged with assaulting a reporter, but said he will leave it up to Montana voters to decide whether they want him to serve in Congress.

"I do not think this is acceptable behavior, but the choice will be made by the people of Montana," Ryan said during a press conference in Washington.

"There is no time when a physical altercations should occur with the press and just between human beings. So that is wrong and it just should not have happened…I think he should apologize."

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A Montana sheriff charged Gianforte with misdemeanor assault Wednesday night after a newspaper reporter said the politician "body slammed" him.

Gallatin County Sheriff Brian Gootkin said Gianforte was charged Wednesday night following a physical altercation that sent Guardian journalist Ben Jacobs to the hospital. The incident occurred hours before polls opened Thursday in the race between Gianforte and Democrat Rob Quist for the state's open House seat.

Democrats immediately demanded Gianforte withdraw from the race, while three of the state's largest newspapers rescinded their endorsements of the GOP candidate.

But a defiant Gianforte portrayed himself as the victim, with a spokesperson blaming "aggressive behavior from a liberal journalist" for the incident at a campaign stop in Bozeman.

The race had already become a national battleground over President Donald Trump and his plan to repeal and replace Obamacare.

Jacobs earlier told MSNBC's Chris Hayes that he was trying to ask Gianforte about the Congressional Budget Office's financial analysis of the Republican health care plan when "the next thing I know, I'm being body-slammed."

"He's on top of me. My glasses are broken," Jacobs said. "It's the strangest moment that's happened in my entire life reporting."

An audio recording of the event and the eyewitness account of a Fox News crew that happened to be in the room support Jacobs' claims.

@Bencjacobs: Greg Gianforte just body slammed me and broke my glasses

Sheriff Gootkin said Jacobs fell on his elbow, but that the injuries did not warrant a felony charge. Gootkin, responding to comments made on social media, acknowledged he gave $250 to Gianforte's campaign in March but said, "This contribution has nothing to do with our investigation which is now complete."

In a statement, Shane Scanlon, a spokesman for Gianforte's campaign, alleged that Jacobs crashed an interview Gianforte was giving to another reporter "and began asking badgering questions," adding that "Jacobs was asked to leave."

"It's unfortunate that this aggressive behavior from a liberal journalist created this scene at our campaign volunteer BBQ," he said.

"The only thing in the Gianforte statement that is factually correct is my name and my place of employment," Jacobs said on ABC's "Good Morning America" Thursday.

In a statement, Lee Glendinning, The Guardian's U.S. editor, said that the newspaper was "deeply appalled" and that "we stand by Ben."

@wabermes: Gianforte sitting in a Jeep. Sheriff's deputies were talking to him earlier. Now a medic is at the window talking with him. #bdcnews #mtal

Polls in the race have consistently shown Gianforte favored to retain the statewide congressional seat vacated by Interior Secretary Ryan Zinke. But Quist, a folk singer, has come within striking distance thanks to an outpouring of money and energy from Democrats desperate to score a victory against Trump.

While the incident could damage Gianforte, it likely came too late to have any major impact on Thursday's election. News broke after Wednesday evening's newscasts, leaving little time for word to reach voters, though the incident dominated newspaper front pages Thursday.

As many as two-thirds of voters have already cast a ballot in the race, according to analysts taking advantage of the state's expansive absentee voting laws.

Unlike other states, Montana does not allow voters to cast a new ballot on Election Day if they change their mind from how they voted early.

The Billings Gazette, one of three newspapers in the state to pull their endorsements for Gianforte, called for changing that law.

@aseitzwald: The front pages voters in Montana are waking up to on Election Day.

Quist initially steered clear of the incident. "I'm just focused on the issues that are facing the people of Montana," he told reporters.

But other Democrats moved quickly to try to capitalize on the moment, running Facebook advertisements in the state aimed at reaching Democratic-leaning voters who have not yet cast a ballot.

The official campaign arm of House Democrats called on Gianforte to exit the race while Democratic National Committee Deputy Chair Keith Ellison told NBC News the Republican should withdraw so he can "focus on his legal problems."

National Republicans, meanwhile, were mostly silent, other than Ryan.

In audio of the confrontation posted to YouTube by The Guardian, a voice said to be Gianforte's asks Jacobs to speak with an aide. Then loud crashing sounds can be heard.

"I'm sick and tired of you guys! The last time you came in here you did the same thing. Get the hell out of here! Get the hell out of here!" the man yells.

@alexis_levinson: So I was there for this - still am

Gianforte and Jacobs have a history: Last month, Jacobs reported that Gianforte owns about $250,000 in shares in two index funds that have investments in Russian companies that are under U.S. sanctions.

Alicia Acuna, a reporter for Fox News Channel, wrote on the channel's website that she and a Fox News crew were in the room setting up an interview with Gianforte when a man she later learned was Jacobs approached the candidate.

Acuna wrote that when Jacobs persisted with his questions, "Gianforte grabbed Jacobs by the neck with both hands and slammed him into the ground behind him."

"To be clear, at no point did any of us who witnessed this assault see Jacobs show any form of physical aggression toward Gianforte, who left the area after giving statements to local sheriff's deputies," she wrote.

"We cannot condone that kind of violence," the Independent Record said in its editorial revoking its endorsment . "We are also sick and tired of Gianforte's incessant attacks on the free press."

The Billings Gazette editorial board wrote "we're at a loss for words" and "we clearly made a poor choice in our original endorsement."