“When I was young, I was a Democrat because I wanted to help people,” says Sean Bielat, who is running to replace Barney Frank in the US House of Representatives. “Now I’m a conservative because I want to help people.”

Bielat is a whip-smart 35-year-old Marine, a successful business manager, and a first-time candidate for Congress out to topple the 29-year incumbent whom many consider the face of liberal Washington arrogance. Mission impossible? Eight months ago, a political thunderbolt electrified Massachusetts and put Republican Scott Brown in Ted Kennedy’s old Senate seat. Bielat aims to induce that lightning to strike again.

Frank was first elected to Congress in 1980, and — with one exception — his reelection ever since has always been a forgone conclusion. The exception was 1982, when redistricting forced him to run against a longtime incumbent, Republican Margaret Heckler — and two-thirds of the newly configured 4th Congressional District came from her old territory. Many people, Frank included, assumed Heckler couldn’t lose. “If you asked legislators to draw a map in which Barney Frank would never be a congressman again,” he said sourly, “this would be it.” But he did win, proving (1) that Frank doesn’t know everything, and (2) that even in Massachusetts, the right candidate at the right time can send an entrenched incumbent packing.

Is Bielat the right candidate to topple Frank? He certainly isn’t typical of the sacrificial lambs the GOP has put up in years past. For one thing, he’s a former Democrat: As a Georgetown undergrad in the mid-1990s, he interned at the Democratic Congressional Campaign Committee in Washington. But his views shifted — slowly at first, during four years of active duty in the Marines (he remains a major in the Marine Corps Reserve), then more decisively at the Kennedy School of Government at Harvard.

“That was very transformative,” Bielat told me last week, as I followed him on the campaign trail in Taunton. Having gone from the “very conservative environment” of the military to Harvard’s “very liberal environment, I was playing devil’s advocate on every single issue. And before long, I found myself thinking that conservative ideas are actually a lot more sound — they’re more cohesive, they make more sense.”

In particular, he came to understand that “market-based solutions are ultimately more sustainable. Government-based solutions, no matter how well-intentioned, no matter how smart the people trying to execute them — if they’re a market intrusion, if they interfere with a functioning market, they fail. They’re not sustainable. They destroy value.”

Bielat points to Frank’s long and ardent defense of Fannie Mae and Freddie Mac, and to their role in the subprime mortage meltdown, as a classic example of the destruction that can ensue when government prevents the market from operating rationally.

The root of the crisis, he says, was the government’s push to expand homeownership, with Fannie and Freddie coaxing uncreditworthy borrowers into mortgages they couldn’t afford. “Barney Frank advocated very hard for policies that allowed just that,” Bielat notes. “He said we should ‘roll the dice’ in favor of expanding homeownership,” even if that meant risking financial soundness and safety.

Bielat (who is opposed by perennial candidate Earl Sholley in the GOP primary) would repeal Obamacare, favors peace through military strength, and wants the Bush tax cuts extended — all mainstream Republican views. Yet he is neither libertarian purist nor far-right conservative. He faults Republicans, for example, for not taking environmental issues more seriously. He wants Congress to reclaim its constitutional responsibility to declare war. To preserve Social Security, he envisions a bipartisan package of fixes — not just private savings accounts, but also means-testing benefits, raising the retirement age, and lifting the income cap on Social Security taxability.

Issues aside, it would be hard to imagine an incumbent and challenger more dissimilar in style and personality than Frank and Bielat. The incumbent is a political lifer; the challenger believes in political turnover (“two or three terms, then up or out”). The incumbent is notoriously peevish and rude; the challenger is sunny and courteous. The incumbent prides himself on not suffering fools gladly; the challenger knows that he can learn even from people he disagrees with.

Can Barney Frank be beaten? It’s a long shot, no question. But even in Massachusetts, long shots have been known to pay off. Just ask Senator Brown.

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