INDIANAPOLIS — Democrat Joe Donnelly triumphed Tuesday in one of the nation’s most tumultuous Senate races, capitalizing on fallout over his tea party-backed opponent’s comment that a pregnancy resulting from rape is “something God intended” to capture a seat that just a year ago looked to be a lock for Republican U.S. Sen. Richard Lugar.

Donnelly beat state treasurer Richard Mourdock after a bruising campaign that saw outside groups pump millions of dollars into the state in a race viewed by many as a test of the tea party’s strength.

In Cass County, however, Mourdock garnered 6,613 votes to Donnelly’s 6,315. Liberatarian Andrew Horning received 1,133 in Cass County.

The victory was a coup for Democrats, who had been waiting years for a shot at the seat. Lugar was so popular that in 2006 Democrats decided not to challenge him.

Even a year ago, Lugar seemed a safe bet to win a seventh term, despite widespread conservative anger with the veteran statesman’s votes on divisive legislation and his support for President Barack Obama’s Supreme Court nominees. But questions about Lugar’s residency combined with a flood of outside spending by groups such as the anti-tax Club for Growth carried Mourdock to a 20-point victory in the May primary.

Democrats pounced on the opportunity as Mourdock made a series of quick missteps that alarmed more moderate Republicans. In a series of interviews the day after his primary victory, Mourdock said compromise should consist of Democrats bowing to Republican demands and stood by tea party views popular with the base of conservative voters, but not the general populace.

“To me the highlight of politics, frankly, is to inflict my opinion on someone else,” he told MSNBC the day after the primary.

Mourdock later tried to tack back toward the middle with declarations that he could work with Democrats, but he stumbled again in a televised Oct. 23 debate when he explained his opposition to abortion except in cases in which the mother’s life is in danger.

“I struggled with it myself for a long time, but I came to realize that life is that gift from God. And, I think, even when life begins in that horrible situation of rape, that it is something that God intended to happen,” Mourdock said.

Republicans, including presidential nominee Mitt Romney, initially distanced themselves from Mourdock but later walked their criticism back, with many saying they didn’t agree with his statement but supported Mourdock’s candidacy.

Democrats spent millions of dollars flooding the airwaves with those comments and other statements by Mourdock in a bid to attract disillusioned Lugar supporters.

For all the Mourdock campaign said about the comment not mattering to voters and arguing that the electorate was more concerned with “Obamacare” and federal spending, voters said it still weighed on their minds in the voting booth.

Kaye Young, 78, of Indianapolis voted for Lugar in the primary and said she thought it was “a shame they kicked him out.”

She said Richard Mourdock “irritated the tar out of me” with his comment on rape. But she still voted for him.

“I don’t want a Democrat in there,” she said. “I’m against Obama and Obamacare. I don’t think Obama has done a good job.

The comment came to be the defining moment of the race. A Howey/DePauw University Battleground poll taken Oct. 28-30 showed Donnelly breaking open a double-digit lead over Mourdock.

“Candidates really matter in Indiana, they (voters) want a good, common-sense approach. They don’t like candidates too far in either direction,” said Christine Matthews, a veteran Republican pollster who conducted the Howey/DePauw poll with Democratic pollster Fred Yang.

“Mourdock was just too far out there, there was just a sense he’s too far outside the mainstream,” she said.

National Republicans descended on Indiana late in the battle after it became apparent Mourdock was in trouble, sending national staff and Republican senators, including National Republican Senate Committee Chairman John Cornyn, to campaign for Mourdock.

The Donnelly campaign, meanwhile, ran a steady, largely mistake-free race, consistently boxing in Mourdock as a tea partyer and getting ads up early to define Donnelly as a moderate Democrat in the mold of former U.S. Sen. Evan Bayh.

Indiana’s Senate battle was the most expensive the state ever has seen, topping $25 million spent on air by outside groups and the campaigns.

Donnelly now becomes the new standard-bearer for Indiana’s Democrats, whose statewide successes almost exclusively have stemmed from the Bayh family. Mourdock, meanwhile, joins the ranks of tea party candidates who ousted moderate Republicans in primaries but could not find enough support among the general electorate.