At "that time he was just a couple of months back in from Iraq, and no one really knew who he was," Rayman, the campaign manager, said in an interview with ABC News. "But we had a couple thousand people at [the town halls] and that was the tipping point. ... I think that was the point at which people stopped talking about the primary and started more focusing on the general election."
In February 2010, Kinzinger, facing only token opposition in a five-way Republican primary, won a resounding 64 percent of the vote.
As Americans across the country slowly soured on Democrats, Kinzinger's momentum built.
Illinois' 11th Congressional District "really closely tracks the national vote," said Tari Renner, a professor of political science at Illinois Wesleyan University, which sits in the district.
Kinzinger was buoyed by Republican victories in November 2009 and by Sen. Scott Brown's game-changing win in Massachusetts in January 2010, even though voters had doubts about whether the GOP streak would last.
"Everybody would ask me, this looks like good momentum for conservatives, but it's not going to last. And I remember thinking, 'You know what? I think it is going to last,'" he said.
Kinzinger racked up three big endorsements from potential 2012 GOP presidential candidates in March and April: Former Govs. Sarah Palin and Mitt Romney, and Gov. Tim Pawlenty all threw their support behind him.
But as much support as he got, the election was destined to be more about Rep. Debbie Halvorson than it was about Adam Kinzinger.
"Halvorson didn't connect very well with the district," said Renner, the Illinois Wesleyan University professor who was the Democratic nominee for Congress in Kinzinger's district in 2004.
According to Renner, Halvorson's voting record was an albatross. "Some of the things, particularly cap-and-trade and health care, were unusually unpopular here."
She was "the incumbent in a year where people are really scrutinizing D.C.," said Isaac Wood, House race editor at Sabato's Crystal Ball, part of the University of Virginia's Center for Politics. Since voters were "listening pretty closely, you have to really sway them, and she wasn't able to do that. If they've got another option that looks pretty appealing, they'd be willing to jump ship, and that's what happened in this race," he said.
In a political atmosphere crammed with policy debates -- health care, climate change, financial regulatory reform -- Halvorson seemed to have difficulty exuding expertise on the issues, analysts said.
"She never found a way to convince constituents that she actually understood matters of public policy, either their details or the nuances of the debates surrounding them," said Greg Shaw, another professor of political science at Illinois Wesleyan. "This severely limited [Halvorson's] ability to defend Democratic positions."
Halvorson had voted in favor of the health care bill, cap-and-trade and the stimulus. When voters went to the polls Nov. 2, she came away with 43 percent of the vote, against Kinzinger's 57 percent.