Republican businessman Mike Braun defeated incumbent Democratic Sen. Joe Donnelly in one of nation's most bitter and hotly contested Senate races.

Braun was leading with 54 percent of the vote to 42 percent with 59 percent of precincts reporting. Libertarian Lucy Brenton trailed with 4 percent. The Associated Press called the race for Braun at 9:27 p.m.

The result defied polls that for weeks said the race was too close to call.

Donnelly called Braun to concede and delivered a less than two-minute speech to Democratic supporters at the Hyatt Regency Indianapolis. He pledged a smooth transition.

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"I'm the luckiest guy in the world," Donnelly said.

After defeating two incumbent congressmen in the primary, Braun denied a second term to the Democratic senator. He ran as a reliable Republican vote who would back President Trump, defeating Donnelly's message of bipartisanship.

Braun delivered his victory speech at the state Republican gathering at the JW Marriott beside his wife, Maureen. The GOP also was celebrating its successful defense of seven of the state's nine Congressional seats.

“I want to thank all Hoosiers for giving me a resounding victory — putting your faith in me," he said. "I will not let you down. I promise.”

He said he'd like to see political races become less nasty, a notable call after months of negative advertisements from both sides.

"It should be about what you bring to the table," he said. "I hope that changes down the road."

Both sides react

Judging from early returns in Marion County, it appeared Donnelly struggled to get out his base.

"It looks like Joe Donnelly's attempt to run to the middle turned off his base in a way that was detrimental to him," said Andy Downs, director of the Mike Downs Center for Indiana Politics. "Donnelly beat up on the far left quite a bit and there were voters across the state who were turned off by that and did not want to hold their noses and go out and vote for him."

Downs speculated that Democrats may need a new game plan to win in Indiana. Former governor and senator Evan Bayh lost the 2016 senate race to Republican Todd Young after employing much the same strategy.

"I think there is something to be said for a less moderate Democrat being a viable candidate," Downs said, "but there has to be something else about the person. With Obama in 2008 it was a message of hope and change and something new and exciting."

Indiana Republicans celebrated the victory.

"The takeaway is this looks great for Republicans generally and it looks great for Mike Braun, more specifically," said Sen Todd Young. "This is all a function of our economic successes over the last couple of years and the fact that Mike Braun’s run a great campaign."

Vice President Mike Pence tweeted his support.

"Good work Indiana on electing @Braun4Indiana as the next Senator from the Hoosier state!" Pence tweeted. "Mike Braun will make us proud in Washington & will FIGHT for @RealDonaldTrump’s #MAGA agenda. I look forward to working with him!"

Donnelly spoke to supporters with his wife, Jill, by his side. He thanked his family and his staff and said the people of Indiana are wonderful. He quoted Martin Luther King Jr., saying everyone is in the same boat, we all have each other's backs and the future is unlimited.

“We love this country so much," Donnelly said. "We need to make sure we work to bring our country together, rather than to divide it, to make sure every American has a chance.”

What led up to Election Day

Donnelly and Braun have been canvassing the state for months trying to get their political bases to the polls, scrapping for undecided voters and attracting high-profile politicians to help them make their case across the state.

With control of the Senate at stake, the race put Indiana in the national spotlight.

President Trump held rallies for Braun Friday in Southport and Monday in Fort Wayne, stoking fears of illegal immigrants, a migrant caravan a thousand miles south of the Texas border and Democrats implementing a socialist agenda after retaking control of the House and Senate.

Obama campaigned for Donnelly Sunday, urging voters to choose hope over fear, to cast a ballot as a check on what he called bad behavior.

They were not the only heavy hitters. Vice President Pence, the state's former governor, campaigned for Braun. So did Sen. Lindsey Graham and Freedom Caucus Chairman Rep. Mark Meadows. Former Vice President Joe Biden, Sen. Cory Booker and Indiana Pacer Victor Oladipo rallied for Donnelly.

Campaign funding has poured into the state, overwhelming Hoosiers with a barrage of TV, radio and digital advertisements.

The candidates and outside groups committed $36.4 million on advertisements for Sept. 30 to Nov. 6, among the highest in the nation's Senate races, according to a USA TODAY analysis of data from Kantar Media/CMAG.

Donnelly raised $4.6 million from July 1 to Oct. 17. Super PACs spent $8.8 million to support him and the Democratic Senatorial Campaign Committee spent another $5.2 million, according to a USA TODAY analysis.

Braun loaned his campaign nearly $4 million through the same period. He raised another $4.5 million. Super PACS spent $9.9 million to back Braun and the Republican Senatorial Campaign Committee spent $2.3 million, USA TODAY reported.

While Donnelly and Braun painted each other as extremists, the political reality was there wasn't that much room between the two.

Braun sold himself as an outsider in the image of Trump and a reliable Republican vote. Donnelly has said he voted with Trump most of the time, when, as the senator liked to say, Trump was with Hoosiers.

Their strategy made sense in Indiana. Trump won the state by 19 percentage points in 2016 and the roaring crowds at his last two rallies proved he's clearly still popular with the Republican base.

Perhaps with that in mind, Obama and Biden held rallies in Gary and Hammond in northwest Indiana, far from the swing voters around Indianapolis.

A change back to norm and an unlikely senator

Braun's victory brought the only statewide office Democrats held in Indiana back into the fold for the GOP. He said he would take to Washington, D.C. what works in the real world.

"We have a narrow window," he said. "We’ve got two years to show that as conservatives we can make things work. We need to get our president re-elected."

Donnelly was in many ways an unlikely senator. After Republicans gerrymandered his House district in 2012 to lean more to the right, he decided to run for longstanding Sen. Richard Lugar's seat.

With help from the tea party, then State Treasurer Richard Mourdock beat Lugar in the GOP primary, angering many moderate Republicans and seemingly giving Donnelly a chance. He won 50 percent to 40 percent after Mourdock's candidacy imploded that October when he described pregnancy resulting from rape as "something that God intended."

Since then, Donnelly has tried to walk the political tightrope successful Democrats must navigate in red-leaning Indiana — voting and sounding conservative enough to reach moderate Republicans and progressive enough to motivate his base.

Donnelly’s loss puts Democrats in a tough spot. After Donnelly leaves office, Democrats will hold no statewide offices and will have deep minorities in both chambers of the Indiana General Assembly. It’s unclear what their path back might look like.

“Joe Donnelly is one of the hardest-working public servants I’ve ever seen,” Indiana Democratic Chairman John Zody said. “I watched him work the last six years in the Senate. So it is a very tough loss, I think. Because I know him, I think it’s a tough loss for Indiana, too. Because he fought for us there.”

Call IndyStar reporter Chris Sikich at 317-444-6036. Follow him on Twitter: @ChrisSikich.