In Indiana Senate primary, a Republican fight over who is the Trumpiest of Trump supporters

INDIANAPOLIS -- In Indiana, a state that’s known for its “Hoosier hospitality,” one of the nation’s most bitter and personal primaries is coming to a head today.

The Republican Senate primary field includes two sitting congressmen and one millionaire business owner who are duking it out for the chance to unseat incumbent Democratic Sen. Joe Donnelly in November.

The race to the finish line is not solely a partisan endeavor — over the course of the primary season, the battle has become as much about toppling their Democratic opponent as it is about backing President Trump. As voters head to the polls on Tuesday, they’ll have to decide which brand of the Trump agenda resonates the most in Indiana.

Congressman Luke Messer says his focus is on bringing the policies of the Trump White House to the forefront of the policy conversation in Indiana.

“We tried to make our campaign about the substance of the Trump agenda,” Messer said in an interview with ABC News. “As I travel our state, that’s what Hoosiers are focused on, they care a whole lot more about the substance of this President’s agenda than they do the style of any tweet.”

Messer represents Indiana’s 6th Congressional District, previously occupied by Vice President Mike Pence before he became Indiana’s governor. Among other Republicans now running to take over that seat is Greg Pence, the vice president's older brother, who has never run for office before but has said he holds the same political beliefs as his younger brother. Messer has donated to Pence's campaign though his political action committee.

Earlier this month, Messer also formally nominated President Trump for the 2019 Nobel Peace Prize . Trump has yet to meet with Kim Jong Un, but Messer already credits his leadership on the global stage with “bringing peace to the Korean peninsula.”

“Peace through strength is working, and the South Korean President Moon Jae-in has acknowledged President Trump should get the Nobel Peace Prize,” Messer said to ABC News in a statement.

His fellow Republican congressman, Rep. Todd Rokita, is taking a different approach.

“Hoosier voters need to know that they’re going to have a fighter to stand with and defend our President,” Rep. Rokita said in an interview with ABC News. “I think, from going around the state, Indiana voters want someone who is a fighter; not someone who goes along to get along or is a coward or timid to do anything.”

Throughout the primary, Rokita frequently brought a cutout of President Trump to campaign events. His message of being in the president’s corner as a fighter is also highlighted in a series of in-your-face ads.

In one ad, Rokita sidesteps addressing any particular piece of legislation but promises to strongly back the President if he is elected. He closes the ad by donning a ‘Make America Great Again’ hat and saying he will “proudly stand with our President and Mike Pence to drain the swamp.”

In his first television ad of the primary season, Rokita was seen shooting a semi-automatic rifle and declaring himself “pro-gun”, which he says was an intentional visual.

“My ad campaign is very natural, it’s very real and yeah, it’s very me,” Rokita said.

“In my ads, I don’t just talk about the second amendment, I show action and there’s me shooting an AR-15 in my ad and that’s dutifully on purpose,” he added.

As for Mike Braun, the dark horse candidate of Indiana’s primary, this race has been all about drawing a contrast between himself and his competitors by highlighting his history as a business owner rather than a politician.

“Politics shouldn’t be a career, we need folks with real-world experience,” Braun says in one campaign ad, adding that he’s running because “President Trump paved the way.”

Braun extended this message to the optics of his campaign by wearing a casual button-down shirt to each primary debate, rather than suits like his two opponents.

The visual contrast was also the focus of one of Braun’s most memorable ads of the cycle, in which he portrayed Messer and Rokita as identical, cardboard cutouts. In the ad, Braun hits the streets with the cutouts to ask voters if they can tell the difference between the two congressmen.

“How long do I have to be in politics to get a suit like that,” Braun jokes in the ad.

Messer and Rokita each say they aren’t concerned about being portrayed as identical, cardboard cutouts.

“The man is obsessed with cardboard,” Rokita said.

Messer also shrugged off the ad saying, “If Mike Braun is outside anything, he’s outside the Republican Party.”

The stakes for whoever comes out on top on Tuesday are high — President Trump carried the state by nearly 20 points in 2016 and Pence previously served as the state’s governor and congressman. In the days following Tuesday’s primary, President Trump will travel to Elkhart, Indiana to deliver a speech on tax cuts and the economy.

WATCH LIVE TONIGHT: You can watch livestreaming coverage of all the primary action starting at 7 p.m. ET on ABCNews.com or on the ABC News app available on the Apple App Store, Google Play Store, Apple TV App Store, and Roku Channel Store.

Don’t forget to sign up for Midterm Elections Alerts to get more coverage of this year’s election season from our powerhouse politics team.