Rep. Scott Peters

In 2012, Democrat Scott Peters defeated incumbent Republican Brian Bilbray in California's unpredictable 52nd Congressional District. (Don Bartletti / Los Angeles Times)

If there is such a thing as an "average" congressional district, it is not California's 52nd.

Covering a northern swath of San Diego, along with the upscale suburbs of Poway and Coronado, the district is home to an impressive list of higher-education institutions, Navy and Marine Corps bases, and acres of tidy business parks with biotech and high-tech companies.

It also has another distinction. Although most congressional districts nationwide are safe for incumbents, the 52nd is anything but.

In 2012, Republican incumbent Brian Bilbray was defeated by Democrat Scott Peters, an environmental attorney and former San Diego City Council member.

This year, three fiscally conservative Republicans — a former San Diego City Council member, a former Marine captain, and a trauma surgeon — are looking to unseat Peters.

The 52nd is one of only seven districts in the nation — and the only one in California — rated as a "pure toss-up" by the nonpartisan Rothenberg Political Report. Registration is closely divided: 33.8% Republican, 32.3% Democrat, 28.7% independent.

Republicans might be poised to reclaim the seat as the economy struggles, and President Obama is plagued by sagging poll numbers and the controversy over Obamacare. Turnout in the June primary and November runoff will be low to modest, which should help Republicans.

The leading Republican challenger is former Councilman Carl DeMaio, a self-described "new generation Republican" and "libertarian-oriented guy."

A transplant from Washington, D.C., DeMaio was elected to the council in 2008, where he was a major force in calling for public-employee pension reform and outsourcing of city services and defeating a proposed sales tax boost. He takes credit for bringing the city back from the brink of bankruptcy — although that assertion is debated.

He lost the mayor's race in 2012 to Democrat Bob Filner but did well in that portion of the 52nd District that is within the city. Not long after his defeat, he began looking at Peters' seat in Congress.

He is a relentless campaigner and fundraiser and a ubiquitous presence on morning television news shows. Recently that has included positive national coverage on Fox News.

"Carl is perhaps the most ambition-driven politician in San Diego," said John Kern, a Republican consultant and former chief of staff to then-Mayor Dick Murphy.

Rival candidate Kirk Jorgensen, 43, a political novice who served with the Marines in Iraq, admits being impressed by DeMaio's energy but annoyed that he won't talk about foreign policy and national defense.

"Carl is a machine," Jorgensen said. "But this election is not about pensions and potholes."

DeMaio, 39, has a well-stocked campaign treasury, the support of the editorial page of the U-T San Diego newspaper and a granular knowledge of the district's voting patterns.

Also, people know DeMaio; in fact, some polls suggest more people know him than know the incumbent.

"Usually one of the tallest hurdles for challengers is [low] name identification," said Nathan Gonzales, deputy editor at Rothenberg. "DeMaio doesn't have that problem."

But with high name identification has come high negatives.

DeMaio had more than his share of political fights: with labor unions and with other council members. He was no favorite of then-Mayor Jerry Sanders, a fellow Republican who endorsed him over Filner through gritted teeth.

"He was the most contentious council member in a long time, he doesn't get along with anyone," said trauma surgeon Fred Simon, 61, who says he is prepared to spend more than $1 million of his own money in hopes of finishing second and making the fall runoff.