This post, originally published Monday, has been updated with the latest news.

The next big anti-Trump battle of 2017 is upon us.

And both parties will have things to prove in Thursday's special election for Montana's only congressional seat.

Up until a stunning turn of events Wednesday night, where the Republican candidate got charged for assault for allegedly body-slamming and — some eyewitnesses said — punching a reporter, Democrats haven't been as bullish about victory as they've been in previous special elections this year. President Trump won Montana by more than 20 points in November, and the candidate Democrats put up to replace Interior Secretary Ryan Zinke, Rob Quist, is a folk singer with zero political experience.

Republicans have been the mirror image: They're pretty sure they're going to win, but they have gone all-in on the race anyway. Vice President Pence and Donald Trump Jr. have been out to Montana to campaign for their guy, millionaire Greg Gianforte, who made an unsuccessful bid in the 2016 governor's race and who, on the eve of the election, allegedly body-slammed and punched Guardian reporter Ben Jacobs. The county sheriff cited Gianforte for assault, and two major state newspapers withdrew their endorsements of him.

We don't know how this 11th-hour news will affect the election. But we do know that the different approaches from each party underscore the same concern for both of them: whether what happens in Montana can build or break momentum for the races that really count, the 2018 midterm elections.

Here are the questions that, no matter the outcome Thursday, each party is likely to be asking itself as the results tally:

Democrats: Could we have done more to help Quist win?

Progressives certainly seem to think so. Quist's campaign raised a remarkable $6 million, mostly from grass-roots donors. Liberal icon Sen. Bernie Sanders (I-Vt.) told a crowd of 3,000 in Butte over the weekend that “the eyes of the country, actually eyes all over the world, are on the great state of Montana.”

Except, apparently, for House Democrats' campaign arm, which gave Montana's Democratic Party some $600,000 for TV ads and not much more.

Charles Chamberlain, executive director of progressive advocacy group Democracy for America, says he feels like establishment Democrats still aren't able to recognize grass-roots momentum when they see it.

“It's really important for the Democratic establishment to stop hedging their bets and limiting themselves,” he said. “They are constantly worried: ‘Should we take this risk? How bad would it look if we did and we lost?’ What looks bad is not even trying, is not fighting as hard as they can in every district across the country.”

On the other hand, polling suggests Quist is behind despite all the help, so why spend precious resources on a risky return on investment, one that Democrats don't even need to try to capture the House of Representatives in 2018?

Win or lose, what's already played out in Montana risks exacerbating Democrats' rifts about how to approach elections in the Trump era, especially now that more seats could be up for grabs than they previously thought — and an assault charge could given them some unexpected momentum.

Republicans: Did we have to do too much to win?

Republicans are not split about how to approach Montana. They've spent millions of dollars and sent some of their biggest stars to the state in an effort to pull out the voters who overwhelmingly went for Trump in November.

Republicans know that if they lose a seat Trump won by more than 20 points, it will be as sure a sign as any that the bottom is falling out from under them, said nonpartisan elections analyst Stuart Rothenberg.

Washington Republican operatives add that this is an unpredictable time in politics. It will be the first major race since House Republicans passed their highly criticized health-care bill. Then came the last-minute surprise: After a blistering Congressional Budget Office estimate arrived Wednesday estimating millions could lose their health insurance from the legislation, Gianforte allegedly body-slammed a reporter who asked him about it.

It's not clear how this sensational story will affect the election. Up until now, Republicans' mantra in Montana was: We'll win, but better safe than sorry.

But how safe do they have to be to hold what has traditionally been a safe seat? Montana will be the third special congressional election this year where a Democrat has made surprising gains in a Republican district. In April, a no-name Democrat came within 7 points of winning a Kansas seat that was one of the most pro-Trump districts in the country.

A week later, a Democrat came within a couple percentage points of winning outright a congressional district outside Atlanta that Tom Price, now Health and Human Services secretary, won by 24 points just a few months ago. (The runoff between Democrat Jon Ossoff and Republican Karen Handel is in June.)

Republicans have had to watch their backs in some of the reddest districts in the nation. And what, if anything, does that say about the 23 congressional districts held by Republicans that Democratic presidential nominee Hillary Clinton won? Democrats need to pick up 24 seats in November 2018 to flip the majority -- nonpartisan congressional analysts at Roll Call just tilted 19 seats in Democrats' favor.

Only time will tell what will happen in the 2018 midterms. But what happens in Montana on Thursday will raise more questions for both parties than answers.