The first meeting between Indiana Treasurer Richard Mourdock and the Club for Growth was a disaster — so it wasn’t necessarily a given that the organization would end up investing $1.7 million and playing such a pivotal role in the conservative challenger’s GOP primary victory over six-term Sen. Dick Lugar.

When Mourdock first interviewed with the conservative activist group in their downtown Washington, D.C., office, he grew testy and even raised his voice at club officials when they peppered him with their standard questions about monetary policy. The interview went so poorly that Mourdock figured he’d never see a dime from the fundraising powerhouse.

“I told my campaign staff all the way along, don’t count on the Club for Growth,” Mourdock said in an interview. “We have to assume the won’t endorse us because that first meeting did go so badly.”

Mourdock and club president Chris Chocola, a former Indiana Congressman, have come a long way since that initial meeting. They only interacted twice since that first interview in January 2011 — including a face-to-face meeting early last summer and a subsequent phone call. But their relationship warmed, and with the club’s crucial financial assistance, Mourdock ended Lugar’s political career on Tuesday.

The deep-pocketed, conservative group’s effect on Mourdock’s rise is undeniable. Even with Lugar’s weaknesses as a candidate, Mourdock’s campaign might have never gotten off the ground without the club’s support.

In April, the club spent more on television in Indiana than the Lugar and Mourdock campaigns combined. In the final 30 days before the primary, the club’s effort made up 40 percent of all independent expenditures in the race.

The club’s endorsement process is a guarded secret. It’s been compared to the movie “Fight Club” — and the first rule of Fight Club is you don’t talk about Fight Club. It’s rare that anyone, especially a candidate, opens up about the process.

But after a Lincoln Day Dinner in Monrovia, Ind., 11 days ago, Mourdock pulled back the curtain on what he described as the club’s unique and effective endorsement process.

Mourdock remains unsure why his first interview went so badly with the club, during which he said he was asked about trade policy with China and the foreign country’s fluctuating currency value.

“I made a couple comments, and it was just amazing to me, that it was like a line drawn between us at that point,” he recalled.

In the following spring months, Mourdock’s campaign struggled. He failed to garner support from other national conservative groups, and his fundraising faltered as a result. Mourdock had raised less than $160,000 after his first quarter of 2011.

Meanwhile, the club focused on other targets such as Sen. Orrin Hatch (R-Utah). They begged conservative Rep. Jason Chaffetz (R-Utah) to challenge Hatch, with a press release declaring, “Run, Jason, Run.”

Mourdock received no such flattering treatment from the club, although he was already in the race by late February. The feeling was somewhat mutual when, in early July, Mourdock suggested to Roll Call that the club didn’t “appreciate” his “ground game.”

Mourdock wanted a second chance to make a good impression on club officials, who granted him a second meeting in early summer. The two parties got along much better this time around, and Mourdock recalled they even gave him a parting gift: a couple of books on foreign currency exchange.

Chocola might not have given Mourdock the benefit of the doubt if he didn’t know him from Indiana GOP circles. Unlike most of the candidates who walked through the club’s door, Chocola knew Mourdock from the Lincoln Day Dinner circuit back home. Club officials talked almost weekly about the Indiana Senate race, keeping a close eye on Mourdock’s progress as a candidate.

“We’ve been watching that race for well over a year, and I’ve known Mourdock for 10 years,” Chocola recalled in a phone interview before the primary. “We just wanted to see a plausible pathway to success, and we saw that there.”

By mid-July, the club mounted its first six-figure advertisement buys of the race against Lugar and Hatch in their respective home states.

In many ways, Mourdock’s relationship with the club proved to be a marriage of necessity, although the two parties could not coordinate because of campaign finance laws. Their goals were inexplicably tied and, therefore, so were their wallets.

Mourdock needed the club’s seal of approval to boost his poor fundraising, which did not improve much over the course of 2011. On the other hand, the club needed a candidate to defeat Lugar, who has a lackluster 65 percent lifetime score on their issues and became their No. 1. target of the 2012 cycle.

Chaffetz declined to challenge Hatch, who is now expected to win his party’s nomination next month. Conservatives failed to recruit a good challenger for their third target, Sen. Olympia Snowe (R-Maine), who announced her retirement earlier this year.

“It’s important for groups like that to take a scalp from time to time so that everyone knows they mean business,” one Indiana Republican operative said.

Finally, for Chocola, the Indiana race was personal. Not only was it his home turf, but Indiana sources say Chocola has had a beef with, in his view, Lugar’s lack of loyalty to Hoosier Republicans. In 2006, Lugar spent $1.6 million on his re-election campaign despite having no primary or general election opponent. That same year, Democrats defeated Chocola and two of his House GOP colleagues in Indiana — and they went down without any help from the Senator.

The final months of 2011 didn’t look good for Mourdock. By the end of the year, he was forced to fund his campaign with $200,000 of his own money.

“I spent months and months making phone calls to people all over the country and I would hear, ‘Has the club endorsed you?’ Well, no they haven’t but I think they will,” Mourdock recalled. “And they just slammed the door right there.”

As late as Jan. 12, Chocola told Roll Call that the club wasn’t prepared to back Mourdock because his campaign was not up to par. The decision point came about a week before the Indiana filing deadline, when Lugar voted with Democrats on Feb. 2 to prevent an earmark ban.

“When Lugar voted against the permanent earmark ban in the Senate, I don’t know if final straw is the appropriate description, but that was kind of a decision point for us,” Chocola recalled in an April 26 interview. “Either we were going to have to get in or not, and we got in.”

A few days after the Feb. 10 filing deadline, the club announced its Mourdock endorsement — much to the candidates’ surprise. There was no heads-up from Chocola or club officials, in accordance with campaign finance rules about coordination. Mourdock read about the endorsement in the news online.

In the next three months, the club became heavily involved in the race. They dominated the airwaves, playing in every major media market in the state and putting out six different direct-mail pieces. Chocola watched the single debate between Mourdock and Lugar from his Florida home.

Most importantly for Mourdock, the money started pouring into his campaign. The club bundled $330,000 for Mourdock, helping him score his best fundraising quarter to date by raising $875,000 through March 31.

“I’m looking forward to after the election, to shake his hand and thank all of them,” Mourdock said. “It’s been much more potent than I ever imagined.”