From left, Republican Senate candidates Luke Messer, Todd Rokita and Mike Braun at a debate Monday in Indianapolis. (Darron Cummings/AP)

One candidate went after his opponent's wife's job. The opponent, in turn, accused him of “lying about my family.” The first candidate fired back that his rival was “unhinged.” Shortly after that, an eight-page memo about what it's like to work for the first guy (always have hand sanitizer) leaked to Politico.

This was all in the first month of what has become one of the most vicious primaries for any party in any campaign in the 2018 election cycle. Nearly a year later, a businessman with millions of dollars to spend on television ads is a last-minute threat to overtake the two bickering members of Congress in the Indiana GOP Senate primary.

Not even Republicans will deny their primary went down in the gutter, fast, and as a result has become extremely unpredictable. As Tuesday's primary looms, there are two outstanding questions: Which of the three embattled top-tier candidates will win? And just how much damage have Republicans have done to themselves as they try to unseat Sen. Joe Donnelly (D-Ind.), one of the most vulnerable Senate Democrats up for reelection in 2018?

The primary will be over Tuesday, but Democrats hope its fallout will continue through November. Here's what you need to know about it:

The players: Two congressmen and a businessman

Todd Rokita speaks at a gun rights rally at the State Capitol last month in Indianapolis. (Michael Conroy/AP)

Rep. Todd Rokita (R-Ind.): He's the one who attacked his rival's wife and whose eight pages' worth of instructions about how to properly ferry him around the district made headlines last summer. Think of him as the outsider Republican congressman: He's been in politics since 2002, and in Congress since 2011, but Rokita has never managed to win over the Republican establishment in Indiana. Now he's using that to his benefit by trying to mold himself as the most Trumpian candidate in the race.

Rep. Luke Messer (R-Ind.): He's the establishment darling. Messer came to Congress in 2012 and was quickly elected by his colleagues to a leadership position. But the only public poll on this race shows Messer behind the other two candidates.

Luke Messer at a February GOP debate in Indianapolis. (Michelle Pemberton/Indianapolis Star/AP)

Rokita and Messer's relationship goes all the way back to when they attended Wabash College together.

Mike Braun: The former state representative and multimillionaire businessman will have thrown $6 million into TV ads, more than Rokita and Messer have spent combined. Republicans familiar with his campaign say he's the front-runner; external and internal polling shows Braun ahead of both congressmen as he makes the case that he's more like Trump than the other guys. Braun ran a clever ad in which he asked voters to tell two cutouts of Rokita and Messer apart.

The punches thrown in the race so far

I'll run this down in headlines, because so much of the three candidates' attacks played out in the press:

City of Fishers pays Rep. Luke Messer's wife $20K per month for legal consulting (Associated Press): This May 2017 article highlighting that Messer's wife is a highly paid government contractor is widely considered the first shot in the primary.

The agonizing, eight-page memo on how to chauffeur a congressman (Politico): This Rokita internal office memo made waves in Washington when it was published in August.

Former aides to Indiana congressman describe toxic work environment (AP): A follow-up piece on what it's like to work for Rokita, describing staffers in tears who walked out of the office and never came back.

Luke Messer didn't disclose DUIs when he replaced lawmaker killed by drunk driver (Indianapolis Star): This dates to 2003, when Messer won a state legislative seat that the Star says helped launch his political career.

Rokita called Trump 'vulgar' in 2016 (Indianapolis Star): The headline from this article, published in early April about a month before the primary, says it all.

Indiana candidate's rhetoric, business record don't line up (AP): This is a report out Wednesday about how Braun, who regularly blasts outsourcing of jobs, owns a company based in Japan that imports goods from other countries.

The fallout

Sen. Joe Donnelly (D-Ind.) in August. (Don Knight/Anderson Herald Bulletin/AP)

I'll let Democrats chime in: “I don't think we could really ask for a better primary,” said an Indiana Democrat granted anonymity to speak candidly about the race.

Sure, Donnelly has a competitive general election ahead of him — Trump won the state by 19 points — but Democrats are grateful that Republicans have done a lot of dirty work for them. When this primary is over, each candidate will have been buried under at least $1 million of negative ads and countless negative news stories.

Republicans argue that Indiana is conservative enough to get over the drama the GOP candidates have inflicted on themselves. Nearly every statewide elected official in Indiana is Republican, and the vice president of the United States is from Indiana. When Donnelly won in 2012, he did it by beating a Republican candidate who made controversial comments about abortion and rape. A Washington Republican following the race closely predicted that any one of the three top-tier candidates could beat Donnelly this fall, even after nearly a year of being busted by one of their own.

But there's no denying that no matter which Republican wins Tuesday, Republicans made this race much more competitive — for themselves.

Correction: An earlier version of this post misstated the date of an Indianapolis Star article about Rokita calling Trump 'vulgar' in 2016 and one element of the eight-page memo about how to work for Congressman Rokita.