Republicans are looking to quash concerns that President Trump is endangering their majority in the House with a special election victory in Montana on Thursday, but their candidate faced a fresh controversy the night before voters headed to the polls.

The Republican nominee in the statewide race for Montana's at-large seat, Greg Gianforte, is favored, but has seen his formidable lead shrink down the stretch. Then on Wednesday evening, Gianforte allegedly "body slammed" Guardian reporter Ben Jacobs. Jacobs posted audio, though not video, of the event. It is being investigated by local authorities, but a Fox News team corroborated Jacobs' account.

Gianforte's campaign issued a statement saying Jacobs shoved a recorder in the candidate's face and the two fell to the ground. "After asking Jacobs to lower the recorder, Jacobs declined," the statement read. "Greg then attempted to grab the phone that was pushed in his face. Jacobs grabbed Greg's wrist, and spun away from Greg, pushing them both to the ground. It's unfortunate that this aggressive behavior from a liberal journalist created this scene at our campaign volunteer BBQ."

Fox News, by contrast, reported "Gianforte grabbed Jacobs by the neck with both hands and slammed him into the ground behind him." The candidate then punched the reporter.

Democrat Rob Quist, aligned with socialist Sen. Bernie Sanders, I-Vt., has raised almost $7 million in the last several weeks, and now threatens to flip a seat held by the GOP since 1997.

"This race would have been over two months ago in a conventional year, where you had all 435 seats in play," Sen. Steve Daines, R-Mont., a close friend and supporter of Gianforte, told the Washington Examiner. "Many believe Montana is this red state, but it bounces back and forth." Democrats control the governor's mansion and one U.S. Senate seat.

The special election campaign for Montana's lone House seat kicked off earlier this year after Republican Ryan Zinke resigned to become Trump's Interior secretary. It eventually turned into another front in the battle for control of the House that has played out in multiple special elections, as Democratic activists energized by their opposition to Trump poured money and manpower into the race.

Montana has not been considered as competitive as the June 20, special election runoff in Georgia's suburban Atlanta 6th Congressional District, where both parties are poised to spend a combined $20 million plus to try and win the seat formerly held by Health and Human Services Secretary Tom Price.

In part, that's because Democratic insiders don't believe Quist is as good of a candidate, or as good of a fit for the seat he is running for, as Jon Ossoff is in Georgia. But as Quist's fundraising from grassroots progressives accelerated, and Gianforte stumbled, Democrats and Republicans in Washington took notice and re-assessed.

"Rob Quist is running an insurgent, grassroots campaign against a well-funded millionaire in Greg Gianforte," Democratic Congressional Campaign Committee spokeswoman Meredith Kelly said. "Montana's special election shouldn't even be on the table, but House Republicans have been forced to spend millions in an attempt to hold onto this Republican seat."

Based on Quist's fundraising and grassroots effort, Democrats otherwise skeptical of their nominee's prospects have opened the spigot somewhat, with the DCCC and House Majority PAC, the super PAC aligned with Democratic leadership, spending more as Election Day approached.

The DCCC will end up spending about $550,000, sources said.

Republicans, concerned after narrowly retaining a conservative Kansas House seat in a special election earlier this year and barely forcing a runoff in Georgia, have been more aggressive, even though Trump won Montana last November by more than 20 percentage points.

Congressional Leadership Fund, the super PAC aligned with House Speaker Paul Ryan, R-Wis., was on track to invest $2.6 million for advertising on television and other media and field operations, including knocking on 100,000 doors across four key counties, and phone bank calls to 300,000 targeted voters.

The National Republican Congressional Committee, the House GOP campaign arm, was to spend around $1.6 million. The White House is doing its part, dispatching Vice President Mike Pence and Donald Trump, Jr., the president's oldest son, to Montana to campaign for Gianforte. The Republican National Committee is involved in voter turnout, and Trump recorded a robocall to encourage GOP participation.

"It's definitely within 5 points," said a GOP operative following the race, on condition of anonymity in order to speak candidly. "There's a very real scenario where it's too close to call on Election Night."

"Gianforte underperformed Trump in 2016 by about 10 percent," this operative added, referring to Gianforte's failed bid for governor. "He had some scar tissue from that campaign. Combine that with Quist's fundraising success and some unforced errors and it goes a long way to explain a large part of the tightening."

It is unclear if the incident with the Guardian reporter will affect the outcome of the race at the last minute. A number of Democrats, including the DCCC, called on Gianforte to drop out.

Montana leans Republican but still elects its share of Democrats to high office. Neither Gianforte nor Quist are a perfect match for state's unique electorate.

Quist's affiliation with Sanders fits with Montana's strong populist strain. Sanders beat Hillary Clinton in Montana durnig the Democratic primaries.

But Democrats that win races tend to separate themselves from the liberal national party on at least one key issue, such as support for the Second Amendment. Quist has not, leaving Republicans reassured that he is too liberal to win on Thursday.

Gianforte is closer to most Montanans on most major issues, such as energy, taxes and regulations. But the wealthy businessman, who moved to the state from New Jersey more than 20 years ago, has an image problem. He can seem out of touch with average voters and has been caught waffling on his support for the American Health Care Act.

Officially, Gianforte opposes the Republican proposal to partially repeal Obamacare, and would have voted against it when it cleared the House on May 4. But he was caught on a leaked recording of a fundraising call saying he was nonetheless glad it passed so that the process of getting to a final bill he could support could continue. The incident with Jacobs came after he asked Gianforte a question about the latest Congressional Budget Office score of the healthcare bill.

Gianforte also is running amid Trump's political stumbles. Republicans claim it hasn't impacted the race. Yet it is perhaps notable that Pence is the chief surrogate from the White House helping out in this campaign, not the president.

"Trump is not as popular as he was on Election Day. But he's still a net positive in Montana. The issue is the Republican nominee," said a Republican insider active in the race.