Republican challenger Keith Rothfus unseated U.S. Rep. Mark Critz in Pennsylvania's 12th Congressional District in Tuesday's election. The district was redrawn during Republican-controlled redistricting.
The defeat was the first for Critz, a Democrat who replaced John Murtha, a veteran Democratic power broker who died in office in February 2010.
Rothfus, a corporate attorney, supports free trade and repealing the health care reform package pushed by President Barack Obama.
Rothfus said Tuesday night his first priority when he arrives in Washington in January will be to make sure small businesses aren't burdened with impending tax increases.
He also touted a plan similar to the one proposed by Wisconsin Congressman Paul Ryan, the Republican vice presidential candidate, which would keep Medicare unchanged for those 55 and older, while making the current form just one of several options available to younger people.
Rothfus, a self-described Reagan conservative, claimed victory after Critz conceded the election.
"We knew we were in it," Critz said. "Turns out we got close, but couldn't go over the top."
Critz said his campaign staff and voters across the district made a considerable effort to secure a win for the Democrats and were confident they could pull ahead.
But the odds were stacked against his campaign, he said.
"The amount of money spent against me and the makeup of the new district was insurmountable," Critz said.
Officials predicted a close race, and at times, Critz and Rothfus were within only a few hundred votes of surpassing each other.
Critz conceded the election shortly before 11:30 p.m. Tuesday. He congratulated Rothfus by social media a few minutes later.
Rothfus championed his "Three R's" while on the campaign trail: a call to repeal Obamacare, reform taxes and spending, and rollback what he described as overbearing government regulations.
The amount of cash dumped into the election overwhelmed the Democrats' campaign, Critz said.
"We knew it was going to be an uphill fight," Critz said.
A graduate of Notre Dame law school and a cancer survivor, Rothfus has run two marathons.
This is his first win in a general election. He lost to former U.S. Rep. Jason Altmire in 2010. Altmire was defeated in the Democratic primary by Critz earlier this year.