The reason Gus Christensen looks like an investment banker is that he was one until four months ago. A handshake reveals a shirt monogram over the wrist, an Omega watch and lapis cuff links he got on a JPMorgan Chase & Co. trip to Chile.

One clue to his new line of work was the Vineyard Vines tie with donkeys he wore to the Yale Club on Feb. 27. Another was his name on the program for that night’s annual Lenox Hill Democratic Club dinner as president and benefactor.

“Reactionary forces are strong,” he told his neighbors from New York’s affluent Upper East Side, their forks and knives clinking as they ate mushroom tart. “But the progressive side is stronger. And both time and right are on our side.”

Christensen didn’t quit banking just to head a local political club. With investors Tom Perkins and Ken Langone comparing the battle against inequality to Nazism, the language they despise is fueling the 42-year-old’s nascent campaign for New York State Assembly, a job that pays $79,500 a year. Money from working two decades on Wall Street will help fund his mutiny against some of its treasured principles.

In his dinner speech, Christensen’s voice lurched and swelled to find the rhythm of the pulpit. He preached stronger rights for workers and women, tougher regulation, cheaper housing and “progress on inequality itself.”

Ayn Rand

Christensen, once a JPMorgan derivatives trader and a Goldman Sachs Group Inc. banker who worked on casino deals, mocked the vanity of Ayn Rand novels financiers adore, put his minimum-wage goal at $15 an hour and praised Massachusetts Senator Elizabeth Warren’s efforts to curb the banks that once paid him.

“I’ve come out of that with a slightly different, or maybe radically different, point of view than a lot of other members of the financial community,” he said in an interview last month. “I may be an idealist whose hopes and dreams are crashed on the rocks of reality in short order.”

Christensen was drawn away from Wall Street slowly. He was bothered by President George W. Bush’s tax cuts for the rich, disheartened by bankers demanding soft regulation and happier volunteering for a friend’s 2012 bid for Congress than he’d been in his day job, he said.

That friend lost to an incumbent, a fate Christensen will avoid. Democrat Micah Kellner, who appealed an Assembly ethics committee decision that he violated its sexual harassment policy, isn’t running for re-election in November. Iraq veteran David Menegon and community-board member Ed Hartzog, both Democrats, are among candidates vying to replace him.